Fusion has been part of the plan for a few days now :) my plan is to make a tile that will hold the first crystal that lands on it, then waits for another crystal to approach. Once both crystals are on top of the fusion tile, they'll simply add together. Then, they'll be released in a direction that will be indicated in the tile art.
I'm hoping to explore my options for a tutorial more, but there will be a point of diminishing returns where it won't be worth explaining every nuance to the player. Hope it turns out ok!