Cast this spell only before the combat damage step.
Target creature gains trample and gets +X/+0 until end of turn, where X is its power. At the beginning of the next end step, destroy that creature if it attacked this turn.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Haste (This creature can attack and as soon as it comes under your control.)
At the beginning of the end step, sacrifice this creature.