Mr. Orfeo, the Boulder

Whenever you attack, double target creature's power until end of turn.

Unnatural Growth

At the beginning of each combat, double the power and toughness of each creature you control until end of turn.

Fling

As an additional cost to cast this spell, sacrifice a creature.
Fling deals damage equal to the sacrificed creature's power to any target.

Soul's Fire

Target creature you control deals damage equal to its power to any target.

Mage Slayer

Whenever equipped creature attacks, it deals damage equal to its power to the player or planeswalker it's attacking.
Equip {3}

Tuya Bearclaw

Whenever Tuya Bearclaw attacks, it gets +X/+X until end of turn, where X is the greatest power among other creatures you control.

Ghalta, Primal Hunger

This spell costs {X} less to cast, where X is the total power of creatures you control.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)

Unleash Fury

Double the power of target creature until end of turn.

Essence Harvest

Target player loses X life and you gain X life, where X is the greatest power among creatures you control.

Zilortha, Strength Incarnate

Trample
Lethal damage dealt to creatures you control is determined by their power rather than their toughness.