This is probably totally wrong, but I recently cut
Forbidden Alchemy because of the decking issue. It gets cast fine the first time, but by the time the owner gathers enough mana to flashback, their library always looks dangerously thin (no doubt in part because that type of durdly Dimir deck tends to draw and loot away a lot of cards).
I suspect
See the Unwritten might run into the same problem in cube. I want to test that effect, though, so I'm trying
Summoning Trap instead (and, instant > ferocious!).