upping the carapaces possibly killed life's chances.
That's not the case here. Keep in mind that a RoL needs to attack first in order to get poisoned by Thorn Carapace and dies after attacking the next turn. That is actually more than enough time (2 turns) to rewind it with an Eternity. Actually, not even Fire Shield would have worked here because it kills the RoL after it attacks, so it still can be reversed by an Eternity. Getting rid of the Eternity is the only way to go here.
However, the upped Spine Carapace shows that team
was waiting for another deck, most likely grabboid rush (because Spine is really good against Graboids, since it blocks both some of their damage and poisons them in return and the poison is carried even if the transform into Shriekers).