({4} magic symbol) minus ({1} magic symbol) for each +1/+1 counter on Workhorse available.
Steps
Activate Workhorse by removing a +1/+1 counter from it, adding ({C} magic symbol) .
Repeat step 1 until Workhorse dies as a state-based action due to having 0 toughness.
Activate Barkform Harvester by paying ({2} magic symbol) , putting Workhorse from your graveyard onto the bottom of your library.
Activate Grenzo by paying ({2} magic symbol) , putting Workhorse from the bottom of your library into your graveyard, and then putting it onto the battlefield with four +1/+1 counters on it due to its static effect.