Kalamax, the Stormsire, and Return the Favor

Prerequisites

• Kalamax, the Stormsire on the battlefield
• Return the Favor in hand
• plus the cost of the additional instant available

Steps

1. Cast any instant by paying its mana cost
2. Holding priority, cast Return the Favor by paying its mana cost
3. Kalamax's first and second abilities trigger
4. Resolve the first ability, creating a copy of Return the Favor and choosing to copy the original Return the Favor
5. Resolve the second ability, putting a +1/+1 counter on Kalamax
6. Resolve the Return the Favor copy, creating a copy of Return the Favor
7. Kalamax's second ability triggers, putting a +1/+1 counter on itself
8. Repeat from step 6 any number of times

Results

• Infinite +1/+1 counters on a creature
• Infinite magecraft triggers