The terminology used in Gems of War is impressively consistent. Once you know exactly what a word means, it pretty much always means the same thing. However with some terms the subtle difference between them isn’t always obvious. The keywords ‘Either’ and ‘Choose’ in spell descriptions are one pair that caused me trouble when I started playing.
The difference between them is that ‘Either’ means that the game will randomly select one of the possible options for you. ‘Choose’ means that you get to select the option at the time you cast the spell. So ‘Choose’ is far more valuable than ‘Either’.
As an example, the spell description for Hellhound says:
Deal [Magic + 4] damage to a random enemy and either Burn or Disease them.
So you don’t get to decide if the (randomly chosen) target gets hit with Burn or Disease.
By contrast, the spell description for Foxglove is:
Choose one: Convert Blue Gems to Green, and Red Gems to Skulls. OR Convert Brown Gems to Green, and Purple Gems to Skulls
So in this case, when you cast the spell you get to choose which pair of gem transformations takes place.
Unfortunately the text isn’t always this explicit. For example, the spell text for Krampus reads:
Deal 28 damage to an Enemy and Submerge them, OR Devour, OR Transform them into a Daemon and knock them to the back.
It should really say: “…and EITHER Submerge…”. Which is logical. Who’d want to Submerge an enemy when you could Devour them?!?