It’s not just the ridiculously high health, damage and immunities, which already make it game breaking.
Also it has ONE counter. Something that it will take 60% of the health off in one hit, which is a separate problem.
On top of that. It slows with double damage/destroys all defenses every second turn. Which means the only thing you can swap to is something that does damage when it is swapped to. It also must defeat it THAT turn, there is a VERY low chance it will survive two shots, no matter what it is.
On top of that, if you’re lucky enough to have thylacotator in your team that match and get bleed off, all the Ardentismaxima player has to do is swap to something that does damage on swap or something that counter attacks. The thylacotator will be defeated, the ardentismaxima will be very much alive and to defeat it after that is VERY costly.
It costs at least 2 creatures to defeat a Ardentismaxima in ANY situation except one where the user leaves it out for the second shot from thylacotator.
In other words, there are about a dozen ways for Ardentismaxima to win the fight and only about 2 ways to defeat it. This is hugely unbalanced. It impacts the entire game.