it's work like discord ability.
Seems more like Nova to me.
It's all true. However (no offence) the game misinterprets the very concept of entropy hugely. Entropy reaches its maximum when all intensive functions of state reach the same value, therefore when everything becomes "average". Actually, the concept of entropy (in thermodynamics) is much more about predictability than about chaos and such.
IMHO, Elements Entropy is a thematic mix of actual Entropy, "Chaos Magic" (aka magic with random effects), and other scientific concepts (such as Schrodinger's Cat).
As for the card itself, it seems to be an way for element to use off-element abilities/cards, as well as strengthening rainbows. (which the metagame still partially favors - I would take that into consideration as a possible balancing factor).