The AI behaves slightly randomly while the player is low level… once you hit level 50 (I think) it straightens out and follows a set (predictable) order of rules:
- match 5 skulls
- match 5 gems
- match 4 skulls
- match 4 gems
- cast some spells (see below)
- cast other spells
- match 3 gems
If more than one 4- or 5- match exists, it will do the one lowest on the board.
Spells have an in-built ‘priority’ that affects the order and chance that the spell is cast. You can only work this out by watching AI teams… Bone Dragon (for example) seems to have very low priority, so AI will always cast any other spell before using that one.
The AI doesn’t seem to intelligently choose which mana colour to take - sometimes it deliberately takes what you need - other times it ignore the only colour it can collect and does something else - so I think this part if pretty random.
AI also choose targets for spells quite randomly (and so stupidly)…