Ice Age

Melee

Cast only on your turn during combat before defense is chosen. Choose how attacking creatures you control are blocked; all defense must be legal. After declaring blocking, untap any unblocked attacking creature. Treat those creatures as though they had not attacked.

Cast this spell only during your turn and only during combat before blockers are declared.
You choose which creatures block this combat and how those creatures block.
Whenever a creature attacks and isn't blocked this combat, untap it and remove it from combat.