Dualcaster Mage, Grimgrin, Corpse-Born, and Return Upon the Tide

Prerequisites

• Dualcaster Mage in hand
• Grimgrin, Corpse-Born on the battlefield
• Return Upon the Tide in hand
• available

Steps

1. Cast Return Upon the Tide by paying its mana cost
2. Holding priority, cast Dualcaster Mage by paying its mana cost
3. When Dualcaster Mage enters, it triggers, targeting Return Upon the Tide
4. Holding priority, activate Grimgrin by sacrificing Dualcaster Mage, putting a +1/+1 counter on Grimgrin and untapping it
5. Resolve the Dualcaster Mage trigger, copying Return Upon the Tide Resolve the Return Upon the Tide copy, returning Dualcaster Mage from your graveyard to the battlefield
6. Repeat from step 3

Results

• Infinite +1/+1 counters on a creature
• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers
• Infinite magecraft triggers