Does not affect Unstable Gas, Rage Potion, Poison, Nightmare
But...But those are all spell damages. I get that you think they'd be OP, but you can't ignore game mechanics and OP combos in order to make a card work.
Unstable Gas: 8-9
+ 5-6
+1 fire + 2 cards + 1 turn of waiting = 40 damage + 2 damage to all creatures on field. Forcing an awkward trio? Check. Very expensive quanta, card, and time wise? Check. Feel free to prove me wrong, but I'm pretty sure a standard UG deck, UP as it is, would be faster than this.
Rage Potion: 8-9
+ 3
+ 2 cards for a +10|-10 or a +12|-12? If you're using Rage Potion as a CC, without Diverge it was already going to kill it probably; if not, it would have been far more worth it to just use 2 Rage Potions instead. As a buff, Rage Potion gets a buff in the world of OTK's and not much else.
Poison: Okay this one's actually fine, doesn't deal spell damage per se, adds poison counters. Sauce: Mirror/Jade shield's do not reflect poison.
Nightmare: Now this is just silly, it's HP draining effects are miniscule, if someone feels like taking the time to gather 8-9
and then 1-2
and play 2 cards for a total of 32 HP (Assuming the opponent has an empty hand, probably much less), then go for it. There are much more cost effective ways to go about damaging the opponent and/or healing oneself.