Infinite Possibilities

You’ve found a way to prepare a spell slot that exists in your
mind as many different possibilities at once. Once during your
daily preparations, you can use a spell slot to hold that infinite
potential, rather than using it to prepare a spell. You can use this
spell slot to cast any spell from your spellbook that’s at least
2 levels lower than the slot you designate; the spell acts in all
ways as a spell of 2 levels lower. You don’t have any particular
spell prepared in that slot until you cast it.