Comments on each.
Mimic: Could be useful, sure, but... it's very brittle and pricy.
Doppelganger: I'd rather use PU, really. Cannot be stopped, doesn't take a turn to execute and is cheaper.
Antigravity: Is alright, dragon combos sound scary at first but shoudl be edible
Pit Viper: Kinda weak and pricy
Blood Asp: Much better, could be a good addon to a Life deck, not specifically poison ones.
Zombie: You're firing Skeletons.
Lich: A very brittle, better Gravyyard.
Archer: On such a brittle creature Sniper is alright. Same for the upgrade, still Paradoxable and under 3 HP.
Ancient Fossil: Yay free Poisons! Also, could be useful sometimes, like for EQ+freePoison+Some Earth deck. Also, there aren't many Earth or Death abilities anyway.
Second Fossil: A pay-to-play Boneyard. Not as useful.
Rusty Automaton: I'd rather use the Hematite Golem, after the fourth turn it's more profitable. This card is like useless.
Goblins: Good idea
Gorgon: I guess the cost is accepTable for a Mono creature.
Medusa: Much better if the enemy doesn't have some supershield.
Shadows: Two for Growth? Other creatures get it for 1. Unfair. Could be useful for one of those Vampire Blessing decks as another beatstick.
Palace Guard: Fairly good idea, damage soakup with the same ratio as Armagio but with the shield.
Paladin: Worse ratio, bigger shield. Could be useful against mobspam.
Giant Squid: I hope you do realize it can only Devour creatures with 1 HP at first, yes? The ability price could be affordable for Mono.
Kraken: Costly, but much better. Could be useful for Water/Earth doing Poseidon and Armoring Krakens.
Apprentice: Just a step for the upgrade, I see.
Necromancer: A very brittle Boneyard. Seeing as both cost 3 Death, I'd rather use Boneyard.
Mage: The ability is too costly for what it does, really. Aside from that, fairly nice but brittle.
Priest: As above. Drop the ability cost to 1 and it'll be perfectly fine, for now it's underpowered because of the high cost.
Overlord: Good card. Really good in Earth/Dark/Quantum deprivation with Devourers and EQs.
Will o' the wisp: Not really useful. Other quantum generators survive longer. Raylights...
Plague Bearer: What's the point of having Skeletons if they die after one turn?
Gravity Bolt: Seeing as there is a way of avoiding Reflega anyway, this card isn't very useful, especially with that Gravity doesn't have any quantum fasteners found in other elements (Brimstone Eater, Immolation, Devourer).
Shield: You ripped this one from Bloodshadow.
Kiteshield: As above.
Buckler: Also, it makes other-element weakshields pointless.
Leopard: Effectively does 9 damage, for 3 Life? Too strong.
Mist Leotard: Effectively does 12 damage and I can't get rid of it, for cheaper than an Immortal from Aether? Too strong, dood.
HEROS
Destroyer: Passive destroying is way too strong no matter what you do.
Unerring: Compared to other heroes, kinda weak. Good creature control, but with two Owleyes I could do the same thing cheaper and with more precision.
Raging: Fast buildup, but expect it to get Paradoxed immediately. Designing a Hero for Fire is hard because the theme makes the Hero easy to lose.
Imperturbable: I guess this one is survivable, stopping up to 4 creatures and no more. An Arctic Octopus can do this thing, just much pricier and is brittle.
Illuminated: 2x SoD + non-instant creature control prevention. Is alright. Pisses Plaguers off.
Avaracious: What kind of a word is that? Also, it might be hard to control out manually, and aside from that it's just a bigger Vampire. Is alright.
Twisted: So, I can end up with a weak thing or a brittle thing, and it drains quanta. Is fairly alright, I guess.
Unstoppable: Momentum on steroids, and... a 6 attacker. Notverygood.
Eternal: You ripped this from Bloodshadow. Also, very good and balanced card, as it can be only delayed and deals high damage, and high damage is what Time needs.
Adam Savage: VERY OP. Does 4 free Snipers at the end of every turn, and can strike Immaterial? Not nice. Would clean out the enemy field immediately.
Foul: VERY OP. The poison will build up really fast. 9 poison, 18 poison, 27 poison... heck, normal poison DECKS don't get to 27, and this can in 3 turns. The other passive effect is a nice concept.
Good thing that they can be Mutated or Reversed, otherwise all of them would be OP. Don't fix this.
If I didn't comment on the upgrade separately, apply the same comment as for the normal version.