Gravitic Punch + Kalamax, the Stormsire + Twincast

Gravitic Punch

Kalamax, the Stormsire

Twincast

How it works

1. Cast Gravitic Punch by paying its mana cost, targeting Kalamax.
2. Holding priority, cast Twincast by paying its mana cost, targeting Gravitic Punch.
3. Kalamax's first and second abilities trigger.
4. Resolve the first ability, creating a copy of Twincast targeting the original Twincast.
5. Resolve the second ability, putting a +1/+1 counter on Kalamax.
6. Resolve the Twincast copy, creating a copy of Twincast, targeting the original Twincast.
7. Kalamax's second ability triggers, putting a +1/+1 counter on itself.
8. Repeat from step 6 any number of times.
9. Once you have an arbitrarily large Kalamax, have the final Twincast copy target Gravitic Punch. This'll create two copies of Gravitic Punch in addition to the original Gravitic Punch.
10. Resolve all Gravitic Punches, dealing infinite damage to each of up to three opponents.