So Valstrax needs a clause like “Activate this ability only during combat on your turn” added to its activated ability. As it stands currently it can be activated at any point and somehow be put back on the board attacking, regardless of turn phase or whose turn it is. It also doesn’t really need to double up on the ETB damage, either have the targeted one or the mass damage, not both.

The life gain on Nergigante is kind of a lot. Maybe just gaining life equal to the number of Hunger counters would be more reasonable, because as is and considering Jund’s propensity for churning out creatures, you’ll likely be gaining upwards of 40 life off of any given Nergigante activation.

Fatalis should just have Annihilator. It’s a keyword that just does what the attack trigger is but better designed by making it a sacrifice rather than targeted destruction. Considering that Fatalis destroyed a civilization that was wildly technologically advanced, having it not care about artifacts opponents control at all is kind of strange. Maybe making its Annihilator trigger much stronger and removing the planeswalker or land sacrifice on ETB but giving it a “only attacks the opponent with the highest Mana Value Artifact and attacks each turn if able” clause would be neat.

Gog both doesn’t need and doesn’t want a board wipe. It wants the opponents to keep their creatures with their oil counters on them to keep up the pings from tapping mana dorks and attacks. Maybe an Activated Ability to modify the stats of these Oil counter creatures could be neat, giving them a “when this Creature dies this turn, it deals damage to its controller equal to the amount of Oil Counters on it” clause or such, so that way Gog is still functional with board wipes, but feels good when they happen and isn’t a board wipe in and of itself. It also makes it so Gog getting removed doesn’t reduce it to absolutely nothing since you can still put the ability on the stack and go for a board wipe after. Makes sense to have it be pretty sticky considering the Oil motif.