Jaws of Defeat

Whenever a creature you control enters, target opponent loses life equal to the difference between that creature's power and its toughness.

Jumbo Cactuar

10,000 Needles — Whenever this creature attacks, it gets +9999/+0 until end of turn.

The Walls of Ba Sing Se

Defender
Other permanents you control have indestructible.

Doran, Besieged by Time

Each creature spell you cast with toughness greater than its power costs {1} less to cast.
Whenever a creature you control attacks or blocks, it gets +X/+X until end of turn, where X is the difference between its power and toughness.