So this idea is actually pretty simple- you know how every school stops using lower level spells at a certain point in the game?
Like, I'm not going to use Dark Pixie or Ghoul anytime soon. Even if I were to get them all maxed out using Spellements, I really have no reason to even put them in my deck.
However, what if I could stack them- like enchanting, but multiple times. I stack the spell, one Dark Pixie on top of the other, in order to create a new spell- Dark Pixie Swarm. The more I stack, the greater the effect. Perhaps it's just a straight damage bonus, maybe it adds a secondary effect like a weakness or a damage over time effect.
Similarly, picture a bunch of Ghouls- all combining their shovels, starting a sort of tug of war, where they all combine their strength to squeeze as much health out of the opponent as possible, falling down at the end, all the shovels collapsing and the health being passed to you. Or maybe they all stand atop each other, like a Cheerleading Squad, and do...I don't know, something.
As the game progresses, as you get more and more useful spells that completely outmode the older ones, they too become stackable. A Covenant of Wraiths, Choruses of Banshees, Fields of Scarecrows, Skeletal Dragon Graveyards; each combining in various ways to various effect.
That way you have a choice- do you start stacking old spells, or do you adopt the new spells for the time being?
Until, in the distant future, many worlds later, they too become obsolete on their own.
