Spellmorph

At-will, reaction, ranged, costs 1 soul shard; when a creature within range casts a spell or uses a power, you infuse it with wild magic, causing it to become a wild surge: instead of its normal effect, roll on the wild surge tables (see the wild-surges section under character basics). The caster's action and resources are still spent.

You can also use this on your own powers as a swift action (no shard cost), embracing chaos deliberately.