Cthulhu might be an animal after Black Dragon and might have a fire whirlpool and it could survive without water for a while and is immune to lava.
TechnicalIt might have a fire whirlpool or an improved ability by the developers
StrategyIt is unknown, but it could stay out of Water for a long time.
People wanted Cthulhu over Black Dragon
They are as big as a whole lava area.