In-game magics are like how they behave in real life, what happens?

[Dr.Archipelago]

What the most usefull magic on war?

Okay, title already told idea of this post soo.I want to speculate what THE MOST usefull magic on war(In War sea or in Mediavel times in general). Acid Ash Crystal Earth Explosion Fire Glass Ink Ice Light Lightning Magma Metal Paper Plasma Poison Sand Shadow Snow Water Wind Wood