Wild Magic Surge

Your commander is a Shaman in addition to its
other types. Shamans you control have:
When you cast an Instant, Sorcery, or Dragon
Spell, you may Sacrifice a creature. If you do,
roll a D20. If the result is Odd, return the
spell to its Owner's Hand. If the result is Even,
copy that spell, you may choose new targets for
the copy.
The power of raw, untamed magical chaos can lead
to great feats of arcane achievement, or catastrophe.