Crime Novelist and Agatha's Soul Cauldron on the battlefield.
Crime Novelist has at least one +1/+1 counter on it.
({1} magic symbol) available.
Steps
Activate Crime Novelist using Triskelavus's ability by paying ({1} magic symbol) and removing a +1/+1 counter from it, creating a 1/1 Triskelavite creature token.
Activate the Triskelavite by sacrificing it.
Crime Novelist triggers, putting a +1/+1 counter on it and adding ({R} magic symbol) .
Resolve the Triskelavite ability, dealing 1 damage to any target.