Activate Soldevi Digger by paying ({2} magic symbol) , putting Workhorse on the bottom of your library from your graveyard.
Activate Grenzo by paying ({2} magic symbol) , putting Workhorse in your graveyard from the bottom of your library, then putting Workhorse onto the battlefield.
Workhorse enters the battlefield with four +1/+1 counters on it.
Activate Workhorse four times by removing four +1/+1 counters from it, adding ({C} magic symbol) ({C} magic symbol) ({C} magic symbol) ({C} magic symbol) .
Workhorse dies as a state-based action due to having zero toughness.