• The glassiest cannon-est glass cannon of Dota.
  
• Spammable spells
  
• Flexible build.
  
• Can be played solo or support
  
• Spells hurts even in late game
  
• Can dominate lanes easily.
  
• Majestic with awesome animations
  
• Sexy, sexy TJ Ramini voice

Pick Skywrath if you:

• Want to nuke people into red puddle in the ground. Or ashes. Or ice shards.
  
• Like birds.
  
• Have weak-to-instant-silence enemies, such as TImber, Three Spirits, Invoker, or Puck.
  
• Have Venge on your team. Lore aside, Venge synergies very well with SWM.
  
• Have squishy enemies, especially on your lane. You work good against Storm, Weaver, QoP, even Invoker and OD.
  
• Desperately need a Nuker.
  
• Have Pugna on your team and want to REKT enemies

Don't pick Bird if

• There are multiple potential Blademail carrier on the enemy team.
  
• There are multiple counters on the enemy team.
  
• You already have a Mid and a #4 support. SWM isn't that good as #5 or #3 offlaner.
  
• You can't play SWM. Bird is love, Bird is life.

Hard Counters :

• Pugna : You cast, you die. But Pugna is like extra extra squishy so don't get caught in Nether Ward range and kill him in 2 seconds.
  
• Spirit Breaker : SWM tend to stick behind his team, but Charge lets Bara close that gap and (even) solo kills you. Also a potential Blademail carrier.
  
• Bloodseeker : SWM hates silences, and Rupture makes kiting far more dangerous. Also a potential Blademail carrier.
  
• Nyxnyxnyxnyx : Nyx is the Boogeyman in SWM's bedtime stories, but Ancient Seal is quite handy if you caught Nyx first.

Mild Counters :

• Razor : SWM has 2 primary single-target spells that proc Unstable Current, and Eye of the Storm eats away your already-nonexistent armor. Also a potential Blademail carrier.
  
• Puck : Could dominate your lane early game and can solo kill you if you aren't careful.
  
• Anti-Mage : SWM can kill Anti-Mage easily but if your attempt fails, Anti-Mage can kill you as easily.
  
• Silences ; Drow, Death Prophet, Doom, Silencer : SWM hates silence but you can silence silencers before silencers silence Dawg you because Ancient Seal has 0.1 cast point while other silences have longer cast points.
  
• Long-range Nukes ; Lina, Lion, Zeus : Bird is also extra squishy so silence and nuke them first. In these fights, the first one to cast a spell wins.
  
• Venge : Other than mental counter, Venge can swap you into the enemy team and reduce your already-nonexistent armor to negative values.
  
• Abaddon : He can dispel Seal on his allies and will be likely to survive your combo thanks to Borrowed Time, but cannot harm you by himself. Also a potential Blademail carrier.
  
• Blademail carrier, unmentioned : Bristleback, Centaur, DOOM, Axe.

Situational Counters :

• Outhouse Denominator : It depends on who dominate the lane first and then snowballs from there, but Bird can win pretty easily.
  
• -armor ; Slardar, Dazzle, SwaggerFriend : One hit from them even in the midgame can cause 200+ damage because your armor is now -20
  
• Sniper : It depends on who kited who but Sniper is also extra squishy, even more with MoM and you can feast on Snipers if they aren't careful.
  
• IceFrog : after he buffs SWM a few times, along with teams overpicking SWM, SWM is now susceptible to the Nerf Hammer.

SWM is an extra squishy caster with relatively long-range spells, therefore he needs to be played carefully, flying on the edge of fights and picking off enemies without getting too close to the fight.

SWM scales well with levels so he is most optimally given a solo lane, but he can also perform greatly as a support and live from kills/assist.

SWM scales prettyREALLY well with INT items. This itemization makes his autoattack hurts more than your average caster but your 0.8 AGI gain limits how well you can use your autoattack.

When the enemy pick Pugna/Nyx to counter you, remember, you can own them first. Just be careful and cast spells when you're sure you aren't affected by Nether Ward debuff. For Nyx, plant sentries whenever you're pushing and be careful when roaming. Nyx has 0.4s cast animation, even if he got Blink DAGAAAAEAEAAAAR[hydra-media.cursecdn.com] You can silence him right when he blinks.

SWM's got one of the highest MS in the game, on par with Lone Druid, Chaos Knight, and lane creeps, inferior only to Luna. Abuse this high MS to run around the edge of the fights. Coupled with Bird's long-range spells (700 range is the least on Ancient Seal), Bird can fly into fights or ganks and leave untouched.

Whenever detection is needed, you might want to buy one for yourself because if you spot a lone enemy, there's an approximately 99,4% chance that you can solo kill them. You can do fine with 350 less gold every 3 minutes by buying sentry and obs, and have that gold back with one kill.


TL;DR
Dont be in the middle of the fights
Careful with Pugna/Nyx
Abuse Bird's high MS and Range to run around.
Detection is key.

• At level 6, Bird's highest damage source is Mystic Flare. Bird had to conserve the mana so Bird can cast it. Spamming Arcane Bolt all willy nilly generally not a good idea.
  
• By taking 3 levels of Ancient Seal, Mystic Flare hurts that it deals almost 600 damage after (regular) magic resistance.
  
• Most of the time, you won't be nuking an enemy all alone, usually you pair it with a stun or another nuke from an ally. Having those skills amplified by 45% hurts more than maxing Arcane Bolt, most of the time.
  
• Leaving Concussive at level 1 and maxing it last (taking a Value Point) has almost the same effectiveness because Concussive is mainly a tool for initiating, long-range slow, or setting up Mystic Flare which usually don't get used so often that it worth the 12s CD over Arcane Bolt or Ancient Seal, depending on which is taken first.
  
• Buying Eul's first provides much mana regen along with powerful utility, as it can make Bird Invulnerable for 2,5s, purge debuffs from you or purge buffs from enemies. The +40MS bonus is also makes you kite easier.
  
• Rod of Atos is nice and perfect companion for Mystic Flare, but if you can position your ult carefully or have an ally with a stun, a mana regen or utility item is better. Also, your nonexistent armor is more of an issue than raw health, as you can quickly silence opposing casters.
  
• This build is even more encouraged on roaming support Bird because the CC (and ampli) from Seal is far, far better than Arcane Bolt from a low-leveled SWM.

Bird has many potential allies, namely :

Disabler-nukers : Lina, Lion, Shadow Shaman, Zeus, Tinker, Venge: All benefit greatly from Seal. Special mention to Lion and SS as they can setup Mystic Flare easier than the others.

Amplifiers : Shadow Demon, Pugna, Elder Titan, Ancient Apparition : All amplifies even more damage which potentially can instagib any target.

Disabler-carries : Faceless Void, Chaos Knight, Naga Siren, Alchemist, MIrana, DK, Sven : All they need to do is throw a disable and get assist/kill gold and sweet, sweet EXP. Special mention to Void because people can't be Force Staff'd out of Chrono. TI4 tryharding, everyone?

Single Target Lockdown : Pudka, Legion Commander, Slark, Clockwerk, Nature's Prophet, Necrolytkaphos : Single targeted stun/trap setups perfect Mystic Flare. Special mention to LC because people can't be Force Staff'd out of Duel and it lets Legion snowball without much farm.

Tank-disablers : Centaur Warruner, Earthshaker, Treant, Roshan : They could initiate and let you throw spells without risk of being targeted.

Outhouse Denominator : late game, Essence Aura can restore 400+ mana per proc (pairs nicely with Bolt) which can mean "let's get Aghanim's Scepter". Agh's Flare can't proc Essence Aura for balance reasons.