All attacks in the game are elemental (things that don't fall under the six elements of fire, ice, lighting, poison, holy, and dark are put in the catch all category of "physical"), and most of the bosses released after like Pink Bean resist every element including physical. I assume the "Elemental Ignore" is there to mitigate the damage reduction from elemental resistances.
Do elements even matter in the game as it is / why do elements still exist if its still poorly explained and uncommonly used?