Classes:

Knight
The Knight is most obviously the tanky one out of your starting Choices. He gets the most increase in Armor per Upgrade, while his Damage is, even though lesss per Upgrade, pretty decent. Most important is that you have no effective Long Range Damage except your charged Attack, cause your Thunderbolt won't Scale into the Late Game very well, which also brings the Downside that many Monsters will get close to you and hit you hard (obviously).

Pros:
-> Cleaves (REALLY Hard. Dont underestimate the Range of you Sword, with enough Knockback you can easily outrange most Monsters)
-> High Armor gain
-> still decent Damage gain (though still quite slow)

Cons:
-> Except charged Attack NO effective Long Range Attacks (The charging being the downpart to this as you can hit only 2 Times if you're
-> Thunderbolt from Stage 6 pretty useless as it scales bad


Mage
The Mage being the Long Range Choice is, in my Eyes, for Starters the bad Choice, as he CAN Range attack, with Range exceeding the Screen, but does so against ONLY THE FRONT MONSTER. Although he has a charged Attack dealing Screenwide Damage like the Knight, he has no effective way to deal AoE Damage early one, even if you go for pure Magic Damage with Crystals. That being said, he still is the Long Range and in later Stages pretty Awesome.

Pros:
-> Long Range gives the Ability to get through Stages with NO Damage Taken (not all, some are just impossible to avoid Damage, especially Boss wise)
-> Pretty good Late Game Choice as Thunderbolt Scales with Both Crystal Magic Up and Wand Damage (Secondary less strong but noticable)

Cons:
-> Missing Armor and AoE make Early Stages Cruel and Painful to get through (especially Bosses)
-> You wil NEED to have Potions ready at all Times to get through the currently highest Stage

Effect Items are sometimes the Key to Victory in a Stage, so here is a short Overview about their most important Characteristics:

-> An Effect Item is 1 Use only, so use them wisely
-> Effect Items Drop randomly from Monsters
-> If another Effect Item Drops while you have one equipped, the alreay equipped one is replaced after a short delay, therefore it is better to instantly use your current Item if you see another one is dropped by a Monster
-> The Damage of Effect Items is a fixed Amount, therefore some loose their Value in Later Stages until you get into Level+ Game

Effect Items:

Orb of Speed (Yellow Orb with Boot)
The Orb of Speed gives you Invulnerability and an insanely increased Amount of Speed upon Use, but it only lasts for about 15% Level Progression. Upon Contact with a Monster, it is dealt the Damage of 1 non-charged Hit and knocked back. You can (and should) still attack while boosted and if Monsters survive they will attack you when you are back to normal again, so beware!

Orb of Charging (Blue Orb with Sword)
The Orb of Charging reduces your Charge Time to about half a Second, therefore giving you the Ability to spam Screenwide Damage over a fixed Duration of Time. As it is a fixed Amount of Time instead of Charges of Use, you should Spam it as much as you can und use it while the Screen is either full or you go against a Boss

Scroll of Destruction (Papyrus Scroll)
The Scroll of Destruction rains Meteors from the Sky, dealing about 1500-2500 Damage after a short Delay to Monsters in the Middle of the Screen. Monsters that are just entering the Screen won't be hit so try to aim a bit before use. As it has a fixed Amount of Damage, It's Value decreases in Higher Stages.

Potion (Potion)
Instantly Heals you for 35% of your Maximum Life.

Mushroom (Mushroom)
Gives you a defensive Boost (Not Sure if Armor Increase or Damage Intake Reduction by a certain Value, but it's not too high so don't expect too much of it). Can sometimes save your Life while being attacked.

Bomb (Bomb)
Throws a Bomb, doing Damage to Enemies it hits and in a small Area around them. As it has a fixed Amount of Damage, it's Value decreases in Higher Stages, but it does quite some Damage more than the Scroll (Probably because it's AoE is just far smaller to balance it's Value). As you literally throw it you have to aim carefully before throwing (Don't misunderstand, you can't actually Aim, but you know where it will land so think about when to use to hit properly).

STILL IN PROGESS

Artifacts are one of the most important Aspects of the Game.
They essentially drop only under 2 Conditions:

1) Killing a Boss
(NOTE: You get a Random Artifact EVERY TIME you kill a Boss, BUT some are Stage Bound (only drop from certain Boss) and some are unable to drop beneath a certain Stage)
2) Random Drop while killing
(the more Rare one, but you can literally get ANY Artifact at ANY given Point in ANY Stage, so Good Luck :))

Artifacts:

Dead Man's Ring - Crit. Chance +X%

Ring of Strength - Melee Dmg +X%

Tome - Magic Dmg +X%

Necklace of Protection - Armor +X%

Tome of the Destroyer - X% Chance your Thunderbolt doesn't cost Mana

Ring of Mana - X% Chance to refill Mana completely upon casting Thunderbolt

Gryphons Feather - X% Chance to Knockback upon critting

Chandelier of Luck - Treasure Chest Gold +X%

Heart-Stone - X% Chance to refill Life completely upon using a Health Potion

Jewel of Protection - X% Chance to be invulnerable for 5 Sec. upon killing a Monster

Ring of Health - X% Chance to refill 10% Health upon killing a Monster

Note that the X-Value depends on the Level of your Artifact (is increased by one when an Artifact you already have drops again)

Following are just some General Tips for you to get into Higher Stages, get through your current Stage easier or just helping you play. Hope you Enjoy the Guide and have Fun ;)

-> You can, at any given Point, "End" the Game, saving your "Inventory" (Amount of Potions, Keys, Life and Mana and current Effect Item) and start another Stage from the Main Menu again with this exact Values (NOTE: Your Stage Progression won't be saved)
-> This gives you the Possibility to revisit earlier Stages to farm up Potions for use in later Stages or Crystals just for Upgrades

-> Don't underestimate Fairies! Their Value increases proportionally to the Amount of successful Hits you do, meaing that the more correct clicks you do, the better/more Loot you get. Fairies are the #1 Source for Keys, easiest to get if you just return to Stage 1 or 2 to ignore the Monsters and focus solely on them as the Monsters don't do any Damage anyway anymore. BUT i would advise you to ignore them as long as Monsters are there in your currently Highest Stage because you'll loose focus on the Threats in front of you (Except you can multitask pretty well but haven't met too many who can do so, so...^^)