The lava spot concept is interesting, however flooding consumes
per turn for a large area outside of the minimal monster spot (limits the amount of monsters the opponent can play),
lava spots should not be permanent creature killing spots (I am assuming they are?)
Instead I can recommend that it lasts for say 2 turns maybe? That way its not just an overly strong altrnative to flooding that is free of maintenance.
Question: How would this work vs pheonix, will pheonix ash die instantly?
Also I think the card is too cheap because it is mono element,
Either justify it by making it duo with another element for the ability or
Increasing cost of upgraded creature at least.
(Think of Otyugh, despite it gaining stats)