Curious Homunculus

If you don't have enough instant and/or sorcery cards in your graveyard as your upkeep begins, Curious Homunculus's last ability doesn't trigger. If you don't have enough as the ability resolves, the ability has no effect.

If an instant or sorcery spell has {X} in its mana cost, choose the value for X first, and then reduce the cost by {1}. For example, Dark Salvation with X chosen as 2 costs {3}{B} to cast if you control Voracious Reader.

Mana from Curious Homunculus's first ability can be spent to cast a spell that has generic mana in its additional cost, such as Borrowed Malevolence with both modes chosen. It can't be spent to pay costs during a spell's resolution, such as the cost Convolute prompts a player to pay.