Cerulean, Roil Keeper

Whenever you lose unspent mana during a precombat main phase, create an X/Y blue
and red Dragon creature token with flying
and haste, where X is the amount of red
mana lost and Y is the amount of blue mana lost. If X is greater than Y, the token has menace. If Y is greater than X, the token
has hexproof. Exile it at the beginning of
the next end step.