Activate Karn by paying ({1} magic symbol) , causing Spawning Pit to become a creature until end of turn.
Activate Spawning Pit's second ability by paying ({1} magic symbol) and removing two charge counters from it, creating a 2/2 Spawn artifact creature token.
Activate Spawning Pit's first ability by sacrificing the Spawn.
The Spawn dies, triggering Pitiless Plunderer, creating a Treasure token.
Resolve the Spawning Pit ability, putting two charge counters on it.
Activate a Treasure by tapping and sacrificing it, adding ({1} magic symbol) .