Tachyon's deck is geared towards cards being in her trash. A good action is usually one that puts a Burst card into your trash, the main ways of doing so are discarding and playing them. Ironically, she can be a bit slow, as getting a lot of cards in trash takes too much time. So she's not recommended for a speedrun. Generally, her Burst cards are a little less powerful than her non-Burst cards as they are designed to be played en masse.

Instead of saying "the number of burst cards in your trash" I'm going to say "burst number".

Lastly, I say "Num: X" in the card descriptions, X is the amount of that card in the deck.

Oh, and shoutout to jagarciao for the hero icons I'm using, they can be found here: http://spiffworld.com/sotm/non-spiff.cfm along with some other cool print and use resources.

Lightspeed Barrage

One-Shot
Tachyon deals 1 target x Melee damage, where x = the number of burst cards in your trash.
Num: 3

This is the big finisher card in Tachyon's deck. The main idea is to get x close to 22 and use extra plays to bring ruin to the villains. Advanced strategies include returning Lightspeed barrage from trash to deck without retuning all the bursts, and playing them over and over. See Argent Adept's Vernal Sonata, Tempest's Reclaim From The Deep, and The Scholar's Don't Dismiss Anything.

Sonic Vortex

One-Shot
Tachyon deals up to x targets 3 Sonic damage, where x = the number of burst cards in your trash.
Num: 2

While not a big finishing move like Lightspeed Barrage, this card has great utility. There are some problems with it, in that it's rarely an even balance of things to hit and bursts in trash, and unless the damage is really necessary or it's the only thing in hand, I'd rather play a burst to have in trash for later. Additionally, you need to not wait on this. If you have more bursts than there are things to hit, the only times that enough targets come into play to use it more efficiently is when something pulls a lot of card from the trash like Forced Deployment or Darken The Skies, or when villains get a lot of extra plays like advanced Apostate or Matriarch.

Hud Goggles

Equipment, Limited
You may play an additional card during your play phase.
Num: 3

An extra play each turn is great while you can support it, and you get an extra play the turn you play this, so, no reason not to. The secret downside is that without extra draws to support the plays your hand will dwindle to nothing in a few rounds.

Pushing The Limits

Ongoing, Limited
You may play an additional card during your play phase and draw an additional card during your draw phase.
At the start of your turn Tachyon may deal herself 2 Sonic damage. If she takes no damage this way, this card is destroyed.
Num: 3

The immediate great thing about Pushing The Limits is that the draw it provides causes it to replace itself, meaning unless something silly happens during the rest of your turn that destroys it, you'll come out even on cards in hand at the end. If there aren't hero damage increases going around, and you are above 10 HP (and you aren't against someone like Iron Legacy or Vengeance Style and even then), you should keep this in play. Especially if there's healing going around. Pushing The Limits is the best way to get your Burst Number up in the long term.

Lightning Reflexes

One-Shot
You may play up to 2 cards now.
Num: 2

I often find that I haven't the cards in hand to use Lightning Reflexes, but when I do, it ends up being a fun turn (and can get a little hard to keep track of on the table top). Often times, after a turn that Lightning Reflexes is played, Tachyon has a hard time getting enough cards in hand to maintain any amount of extra plays, so you really start to appreciate extra draws.

Research Grant

Ongoing
Power: Draw 2 cards.
Discard a card.
Num: 2

Research Grant completely replaces base Tachyon's power, and sum total is +1 card in hand. More importantly it's usually always +1 Burst Number as well. Any Tachyon should keep this in mind when their hand is low (except Freedom 6 Tachyon, F6 Tachyon OP).

Hypersonic Assault

One-Shot
Tachyon deals each non-hero target 1 Sonic damage.
Targets dealt damage this way can't deal damage until the start of your next turn.
Num: 3

Hypersonic Assault is amazing, provided there's no damage reduction (or you can get around that with increases/irreducibility) then the only non-hero targets that can do damage this round are ones that enter play this round. It hard counters reaction damage like Ambuscade's Sonic Mine and Baron Blade's Backlash Field, and buys time to get rid of big threats like Omnitron's Electro-Pulse Explosive. Besides that, it locks down villain character cards, making it super good in a vengeance game, putting a stall on Bugbear's healing. There are minor drawbacks, in that it prevents villains from hurting themselves (I'm looking at you Akash'Bhuta), so look for those situations when using this.

Fleet Of Foot

One-Shot, Burst
Each player may draw a card.
You may play a card.
Num: 3

This card is a big favourite of mine. It's cyclical, adds a Burst to your trash, and there's never a reason to not play it other than punishments for extra draws/plays. Only thing to consider is that it's still in play while the card you play off of it resolves, so it won't increase damage dealt by Lightspeed Barrage unless you manage to put a card play between this and that (for example, by playing a H.U.D. Goggles after this).

Quick Insight

One-Shot, Burst
Draw 3 cards. Discard 2 cards
Num: 2

Assuming you can discard 2 Bursts (and assuming they aren't Fleet of Foot) this card is the fastest way to get bursts into your trash, and it's a net neutral on cards in hand (meaning after your draw you'll have an additional card at the end of your turn), allowing you to play more later with H.U.D. Goggles.

Nimble Strike

One-Shot, Burst
Tachyon deals 1 target 1 Melee damage
You may draw a card.
Num: 3

If you're looking for something to play, Nimble Strike can help you maintain momentum as you get to draw to replace it. Although it only does 1 damage, you can use it to bait redirect effects before landing big hits with cards that use your Burst Number.

Accelerated Assault

One-Shot, Burst
Tachyon deals each non-hero target 1 Melee damage.
Num: 3

Dealing damage to everything is normally a pretty ok thing to do, however, sometimes there are drawbacks like Silver Gulch's Cactus, Glamour, or Greazer's hair. On the other hand, when there isn't a drawback and you have a couple of damage increases from Legacy you can deal out some substantial damage.

Supersonic Response

One-Shot, Burst
Tachyon deals 1 target 2 Melee damage.
If that target dealt Tachyon damage since your last turn, she deals that target 2 Sonic damage.
Num: 2

With the second instance of damage active you can get past "first time I'd be dealt damage" reduction or redirection, like on Biomancer or Spite's PL602 Compound Omicron, and with damage increases you can get to sill levels of damage for 1 play. The problem though is that Hypersonic Assault can frequently stop this card from getting really good.

Sucker Punch

One-Shot, Burst
Destroy 1 target with 2 or fewer HP.
Num: 3

Sucker Punch probably wins the award for "Most Discarded Card" at least for Tachyon. It rarely has use, and even then, you can generally deal the damage to get rid of the target anyway. There are exceptions, like a target that has large damage reduction or Citizen Dawn or Baron Blade becoming immune to damage at 2 HP. Those scenarios are very satisfying.

Synaptic Interruption

Ongoing, Burst
If Tachyon would be dealt 3 or more damage by a single source, you may redirect that damage to a target of your choice and destroy this card.
Num: 3

Playing Synaptic Interruption is a delayed Burst in trash, and is the only Ongoing Burst (which makes calculating Experiment Odds so much harder). It makes for great effect when fighting a heavy hitter like Iron Legacy, or Mad Bomber Blade.

Blinding Speed

One-Shot, Burst
Destroy 1 environment card or 1 ongoing card.
Num: 3

Controlling the environment, can let you control the tide of battle, and dismantling the villain play area is key to victory, though some villains have none, or none that matter, so sometimes you can do without these kinds of cards if the game is short enough.

Regular Tachyon: Rapid Recon(27HP)

Key to using Tachyon is knowing what to discard, most of the time, you can ask whether or not the card is of immediate use, and if not, focus on getting cards in trash. Already have HUD Goggles in play or hand? Discard. Is it a non-Fleet Of Foot Burst? Discard (unless Blinding speed is really needed). You may want to reconsider if you're up against a villain that'll break your stuff, but in general, discarding non-burst cards gets you to burst cards to discard or play quicker.

The Super Scientific Tachyon: Experiment(26HP)

First off, the biggest difference between this and her regular power is the fact that this one can be used on any deck, and I'll talk more about that in the synergies section, here, I want to focus on Tachyon. When used on Tachyon you almost always benefit, and not necessarily by playing cards. Two cards into your trash is better than one, and getting your whole deck in there is what you want. In that regard Super Scientific Tachyon is the fastest of the lot if she uses her power on herself all the time. Her full success odds (which is the odds that the cards get played if experiment is used with every card in her deck) is 51.73%, and there are 5 hero decks with better full deck odds, and some villains to consider using it on, but more on them later.

Freedom Six Tachyon: Team Leader (28HP)

At a cursory glance one might think this power weaker than the others. The character card has more HP, and the power doesn't put Burst cards into your trash. However, the extra card draw lets you use HUD Goggles efficiently from the get go, and providing everyone with extra draws is a great boon as those with more choices minimize the downside to chaos (that's a Slay the Spire reference, not my own line). It does turn Tachyon into a bit more of a support character, but it smooths everyone out really well.

Freedom Five Tachyon: Blitz (25HP)

This power speeds up Tachyon quite a bit because it turns her into a walking finisher. If (X+1)(Y+1) > Z (Where X is bursts in trash, Y is damage modifier per hit, and Z is villain HP) you can end the game immediately, and this power is among the best to get the Living Weapon title with for that reason. Otherwise you can use it to finish targets nobody likes, for example, direct 4 hits at Glamour and she's gone (1 redirected and 3 nemesis increased hits), use against Friction when she has a lot of Surges in trash and was accidentally ignored for a while, use with regular Legacy, and a Ra, with Argent Adept, and Visionary for up to +7 per hit. Unfortunately, cards that say "One hero may use a power now, if that power does damage..." modify it somehow, only work on the first hit, so Hasty Augmentation (from Unity) doesn't overwhelm immediately. The major drawback of this power is that it relies so heavily on Bursts in trash, and depletes them, and is definitely the slowest for getting those bursts there in the first place. Use Completionist Guise to swap her in at the end of the fight however and you circumvent this problem entirely.

Omnitron-X, Fugue State Parse, and The Sentinels' Writhe, all have an innate power that facilitate Tachyons deck by getting cards into trash (or play). The Visionary can help with drawing and discarding as well, and Scholars Don't Dismiss Anything is always a boon, and the putting a card back option can be used to reload a Lightspeed Barrage late in the game (Vernal Sonata and Reclaim from the Deep count too). Setback can help as well, with Fumbling Fool, and Cash Out letting you discard cards. Termi-Nation Bunkers Incapacitated ability (put a deck in its trash) can skip a lot of effort, and Dark Visionary is incredibly useful for getting successful Experiments to happen, given a little bookkeeping. Mordengrad can discard cards for you, and La Comodora: Curse of the Black Spot can too.

Experiment has so much in it that I hit the character limit on a single section with Synergies:

• The Sentinels have a full deck odds of 66.66% (2/3) due to having 32 One-Shots. It's really strong to use Experiment on them, just keep in mind that they've no way to recover lost Signature cards, and you can get two revive cards when nobody on the team is down.
  
• Legacy has a full deck odds of 58.72% because of his 28 Ongoing cards (of which 17 are limited and therefore match with the ring). Good odds of a match, but once most of his Ongoings are in play a lot of them become non-matches due to the abundance of the Limited keyword. On top of that, occasionally you get Heroic Interception, so remember to have him go before Tachyon if you aim to do this.
  
• Setback has 53.33% chance on a full deck, with his 26 One-Shots, just keep in mind that you may cause his lucky pool to fluctuate wildly, or play Ongoings he doesn't need. Most likely though you'll be playing his One-Shots, keep that in mind for Cause and Effect, and Whoops, Sorry
  
• Stuntman has a 52.69% due to a lot of his cards being Limited, the only things to look out for are Coute Que Coute and Hidden Mine when you don't want them, or In Media Res with a non-optimal hero order, but the increased out of turn actions available will be appreciated.
  
• Void Guard Idealist has 51.92% odds with a full deck, and she'll really appreciate playing all those One-Shots she has, and with very low odds of matching The Monster of Id at a bad time, it's pretty reasonable to Experiment with her often, though there is a possibility of getting one of the Concept searching One-Shots when the only one findable in the named zone (of deck and trash, each One-Shot mentions only 1 (they are non-optional)) is the Monster of Id.
  
• This is where Tachyons deck lands with its 51.73%, and we already talked about her.
  
• Scholar is the first below 50% at 49.87% and leans towards One-Shots, and you can start chains by hitting Don't Dismiss Anything, but can accidentally discard his entire hand with Know When To Turn Loose. Additionally, Bring What You Need, can let him tailor the outcome in advance with a little bookkeeping.
  
• The Wraith comes next with 49.62%, and is mostly focused on limited equipment. Besides which, most of her one-shots are less than ideal sometimes (Trust Fund, Suture Self, Grappling Hook, Inventory Barrage), so I'd say, avoid her deck if she's set up.
  
• The Naturalist has 49.23% odds, weighed towards his one-shots, and the only bad things I can see happening is an unwanted Environmental Allies or Indomitable Force (with the optional redirect always triggering because options)
  
• Void Guard Medicos odds are 48.85%, with an almost even split between ongoings and one-shots (19:21 respectively) personally I'm a little bit nervous about playing random card from a deck that likes to hurt its owner, but they don't tend to do more than 2 damage each, so it's generally fine but I still worry about the guy, and I shouldn't unless he's actually low. Watch for Regeneration if the turn order isn't great for it entering on Tachyons turn.
  
• Guise is the first of 2 decks that have an even split of ongoings and one shots at 48.72%, his ongoings are all limited, and whose one-shots are occasionally too situational to be useful. Additionally it can be difficult to balance where he is in the turn order for Selling Out with random stuff coming into play off of Tachyon.
  
• Parse has the other even split deck, which look like a better experiment target, with multiple stackable ongoings, and some more general use one-shots in her repertoire.
  
• Nightmists odds are 48.59% mostly one shots but her remaining cards are mostly divided. This does let her get cards into play while Mist Form is out, but watch for low HP Nightmist being forced to put Oblivion into play (when Master of Magic won't heal her!)
  
• Expatriette will mostly match equipment with her 48.2% so it's a good way to get her jumpstarted and some of her cards appreciate getting ammo into her trash. There's no cards (other than ammo with no guns, and duplicate guns) that do harm to worry about, so work away.
  
• Void Guard Mainstays 46.92% leans towards his Ongoings, but you are almost just as likely to get One-Shots (while there are more One-Shots, the Limited Equipment makes Limited Ongoings more likely by 1-2 percentage points). Even then, it's a bit of a volatile mix, as some of his ongoings are harmful (though it'd be funny for him to put Progeny in a headlock) and some of his One-Shots destroy his own stuff, School of Hard Knocks has each non-hero target hit him. All in all, reasonable odds with painful results.
  
• The Visionary has a modifiable 46.54%, as Foresight can let her stack the bottom of her deck for you, and this lets her get things into play with Telekinetic Cocoon out, but remember Brain Burn if you do a blind Experiment.
  
• Tempest has full deck odds of 45.64%, mostly One-Shots (all appreciated), only possible regret is an accidental double Localized Hurricane, which is mostly only likely if you already have one in play.
  
• Fanatics flat 45% is mostly contributed to by her One-Shots, with 27% that you'll get 2 One-Shots on an experiment, though other than accidentally using Final Dive on a hero, no downsides there. The problem that can occur is accidental Chastise or End of Days (Chastise can be forced to go next to Mobile Defense Platform until the start of Fanatics turn)

• Sky-Scrapers 44.49% is mostly a result of her One-Shots, keep in mind however, that you'll probably switch her size multiple times, which can be of great benefit with Proportionist.
  
• Luminarys 44.1% is reasonably good, but what's better is that he doesn't particularly care if you succeed or not. He likely gets more cards into his trash, which contributes to his endgame.
  
• Lifelines 43.72% is mostly due to his One-Shots, which can play environment cards, discard the top card of each deck, make him hurt himself, heal heroes, and fish out equipment cards. There's a lot he can do, just be aware of the things you don't want.
  
• K.N.Y.F.E. at 43.59% leans more towards One-Shots, the only ones to worry about would be Incidental Contact and For The Greater Good, which damage K.N.Y.F.E. and friends. Her Ongoings are also quite likely to come out and they're all neutral at worst so you're mostly fine to experiment with her. (heh)
  
• Ras 43.08% is a bit skewed compared to what it'd be mid-game because of The Staff of Ra, which leaves his deck really fast because of Summon Staff. There's nothing to be afraid of in the deck (other than something like Imbued Fire vs Omnitron or Scorched Earth with Mobile Defense Platform (the Environment)) and this is a good way to get Solar Eclipse into play out of turn.
  
• Haka having the same odds as Ra is odd, but given they have the same number of One-Shots it's understandable. There are things in Hakas deck to look out for however, such as Rampage at a bad time, or Enduring Intercession with large environmental damage coming that you do not want all of. That said, getting Dominion quicker and playing hakas for draw 2 discard 1 is pretty good to get him going.
  
• Chrono-Ranger's sheer amount of deck searching will quickly make his 42.69% redundant, as he'll have less Equipment and Bounties to dilute his One-Shot focused deck. Watch for Hunter and Hunted.
  
• Captain Cosmics 41.92% chance comes from the amount of Constructs. Watch out for Potent Disruption and Construct Cataclysm, if Cosmic doesn't want them.
  
• Void Guard Writhe has a 40.64% chance of a match. Depending on hero order, giving him opportunities to destroy the Shadow Cloak out of turn can be very advantageous, whereas he might otherwise be afraid to use those effects.
  
• Harpys 40.77% is a dangerous one. Her deck is mostly One-Shots and there's a good chance of getting one that'll make her hurt heroes or herself (Lash of the Elements, Arcane Explosion) and regardless, her One-Shots also tend to flip control tokens, which can spoil her well laid plans.
  
• Bunkers flat 40% is mostly from equipment, but from here on in, I think it might be better to find someone higher on the list. Most of those Equipments are Limited and there's a chance (6.3% of all Experiments on a full deck) that you'll match a Mode card, which can hurt if he wanted the one he already had.
  
• Absolute Zeros 38.58% is indicative of his deck distribution, 15 One-Shots, 12 Ongoings and 13 Equipment is an almost perfect 3 way split. It's aided by the overlap of Limited at some points however, and Experiment can put some Equipment into the trash for Modular Realignment to grab if he's struggling at the start of the game.
  
• La Comodoras 37.56% will feel inaccurate when she starts looking at the bottom card of her deck and using Rudder in the Timestream in conjunction. She'll also set up other people for this at the same time.
  
• Argent Adepts 36.92% is due to his 18 Ongoings and 16 One-shots, the 6 Equipment cards getting in the way a little, and there's no overlap to speak of. the Equipments can be quickly extracted by Instrumental Conjuration, and you can stack the bottom of his deck with Arcane Cadence
  
• Benchmarks 36.03% is due to a 20:11:9 ratio, between Ongoings, Equipments and One-Shots respectively, I feel benchmarks player won't like seeing his Hardware discarded, nor will he enjoy the unpredictability of new software (though the order of start of turn events can let him ignore the result you give anyway)
  
• Omnitron-Xs 33.46% will flux a lot, as they take cards directly from deck and shuffle their trash back in with Reset. If you manage to hit a plating card (and match it) they might get mad at you for doing so, so experiment on the robot with caution.
  
• Unitys 31.79% is tied for second last, due to a close to 3 way split among Equipments, One-Shots and Golems, low odds, although Termi-Nation Unity would like to see Mechanical Golems in her trash early on in the game.
  
• Mr. Fixers 31.79% tying with Unity is because he has a similar split (with different keywords). Mr. Fixer will hate it if you mess up his perfectly good layout though, so I'd just avoid him anyway.
  
• Akash'Thriyas 30.38% comes in last, due to the tree (if it were a seed, she'd be above Mr. Fixer and Unity), though getting seeds into her trash quickly can make her game easier. Try it out sometime.

Tachyon hits a lot of targets for very little (which is a problem when damage reduction or single target villains) and then later deals 1 target for a lot (which can be a bit of a problem in Team villain mode). Consistent damage increases can make her area damage spectacular, and her Hypersonic Assault can make for a nice easy turn (and protects from sonic mines to boot). I mostly consider her to be a finisher, as when you can play 3 Lightspeed Barrages to win, you do that (though sometimes it can be necesary to get rid of something particularly nasty using them). At the end of the day she's a cannon that fires 3 times each game (each Lightspeed Barrage). If you shuffle your trash into your deck and get through it all again, you can count yourself luck to survive that long or you have a great healer on the team.