Dolt, New Cascade Leader

Dolt, New Cascade Leader can't be blocked.
While Dolt is tapped, opponents can't cast creature spells.
{u}{u}{u}{u}, {t}: All other creatures get -0/-X, where X is their respective toughness. Then Dolt gets +Y/+0, where Y is the total of X calculated by this ability this turn, until end of your next turn.