Defeated Smiles yield "thick blood" and "thin blood". Thick blood functions similarly to experience points, and players gain more by shooting Smiles' critical points. The player may redeem thick blood for "serum" while in "Harman's Room", checkpoints that appear throughout the game. Serum is used to improve the attributes of the characters such as "power" and "speed". This also unlocks special abilities for the characters. Players may save their game in designated Harman's Rooms. Thin blood is used to recover the characters' stamina and fuel special abilities.