im confused on how to unlock the third slot
Hey. In this first test version, the third slot unlocks after you've summoned the first 6 tier 1 creatures.
From the gamepage: "There are 6 girls, each with 2 tiers to unlock (so 12 recipes to discover in total). Have fun."
There is nothing in the game for the third slots yet.
The 2-hearts version of each girl needs 3 ingredients.