Agatha's Soul Cauldron + Inquisitive Puppet + Arwen, Weaver of Hope

Agatha's Soul Cauldron

Inquisitive Puppet

Arwen, Weaver of Hope

How it works

1. Activate another creature you control that has a +1/+1 counter on it by exiling it, creating a 1/1 Human creature token that enters the battlefield with at least one +1/+1 counter on it due to Arwen.
2. Repeat using the Human token instead.

This elegant loop uses Agatha's Soul Cauldron to grant the sacrifice-and-create ability of Inquisitive Puppet to any creature holding a +1/+1 counter. Because Inquisitive Puppet exiles itself as a cost to make a 1/1 Human token, and that token immediately receives a +1/+1 counter upon entering thanks to Arwen, Weaver of Hope's passive ability, the resulting token is instantly equipped to repeat the process indefinitely. Agatha's Soul Cauldron also conveniently fixes your mana needs to fund the ability along the way, generating an unbounded chain of entering and leaving the battlefield.