Stalwart Successor, Kithkin Spellduster, and Phantom Train

Prerequisites

• Stalwart Successor on the battlefield
• Kithkin Spellduster on the battlefield
• Phantom Train on the battlefield

Steps

1. Activate Phantom Train by sacrificing Kithkin Spellduster When Kithkin Spellduster dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
2. When Kithkin Spellduster enters, Stalwart Successor triggers, putting a +1/+1 counter on Kithkin Spellduster Resolve the Phantom Train ability
3. Repeat

Results

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