Bartolomé del Presidio, Grazing Kelpie, and Hardened Academic

Prerequisites

• Bartolomé del Presidio on the battlefield
• Grazing Kelpie on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Bartolomé del Presidio by sacrificing Grazing Kelpie
2. When Grazing Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Hardened Academic triggers, putting a +1/+1 counter on Grazing Kelpie
4. Resolve the Bartolomé del Presidio ability
5. Repeat

Results

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