... To have "cross strain" enemies, with both damage and resistance types of the separate monster families? Would it make the game more interesting? Would it make people use more normal damage weapons? Would you enjoy that type of enemy based on it's resistances?
... To have a bomb with catalyzer charge time?
you mean, resistant to elemental + shadow, weak to piercing? only an example.
well, it could be an idea, it would be like: beast fiend / jelly gremlin / undead construct. but only the first seems nearly plausible.
the others are excluded, because they have different weaknesses.