Agatha's Soul Cauldron + Triskelion + Nearheath Stalker

Agatha's Soul Cauldron

Triskelion

Nearheath Stalker

How it works

1. Activate Nearheath Stalker using Triskelion's ability by removing a +1/+1 counter from it.
2. Repeat step 1 until Nearheath Stalker has no +1/+1 counters on it.
3. Resolve all Nearheath Stalker abilities dealing 1 damage to Nearheath Stalker, and any remaining damage to any target(s).
4. Nearheath Stalker dies as a state-based action due to having 0 toughness.
5. Nearheath Stalker's undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
6. Repeat.

This loop turns Nearheath Stalker into a self-sustaining artillery piece by leveraging Agatha's Soul Cauldron to feed Triskelion's activated damage ability into the graveyard. Because Agatha's Soul Cauldron also allows you to spend mana of any color and grants activated abilities to your creatures with +1/+1 counters, Triskelion's pinging power is seamlessly transferred. Whenever Nearheath Stalker runs out of counters and dies, its undying ability triggers to bring it right back to the battlefield with a fresh +1/+1 counter, resetting the sequence for infinite damage and death triggers.