My idea goes along the lines of:
Mage cards have rituals, that are a combination of 0 cost spells that are cast when a few conditions are met
Firstly, a ritual draws a series of magic circles on the board tiles following a survivors pattern, they don't take board space and the circles are through lines like a constellation
The magic circles are various 0 cost spells that activate for the minion occupying the tile, when all the linked circles are occupied by a minion, the ritual will then activate all circles at once, they cast their respective spell on the minion on top of it
If there's multiple triggers on a ritual all must be activated for the ritual to start
If multiple rituals overlap the overlapping circles will merge and become a single bigger ritual
Once fully activated the circles will disappear and the ritual clears




