There are four in game.
You get Moses for defeating the Preists inside the Church.
When you unlock Fartkour, you'll find Gerald on top of the SoDoSopa, give him a vial of cheese and he'll let you summon him.
Either create a macaroni picture to summon Moses or use a cheese Vial by pressing
during combat.
All summons once unlocked are used by
on the D pad.