Play Power Depot, which will enter with a +1/+1 counter on it due to its modular ability
Cast Toph either from your hand or from the command zone by paying 2 plus commander tax if applicable.
When Toph enters, it triggers, earthbending Power Depot and putting a number of +1/+1 counters on Power Depot equal to the mana spent to cast Toph, increased by Brad Boimler.
Activate Shilgengar by sacrificing Power Depot.
When Power Depot dies, its modular ability and Toph trigger.
Resolve the modular trigger, putting the +1/+1 counters that were on Power Depot onto Crystalline Crawler, increased by Brad Boimler.
Resolve the Toph trigger, returning Power Depot from your graveyard to the battlefield tapped. Power Depot will enter with a +1/+1 counter on it due to its modular ability
Resolve the Shilgengar ability.
Activate Shilgengar by sacrificing Toph. Choose to return Toph from your graveyard to the command zone.
Activate Crystalline Crawler by removing a +1/+1 counter from it, adding R/G.
Repeat step 10 until you have enough mana to cast Toph.