The Gensokyo Mod adds 17 new bosses, divided into seven difficulty Tiers.
Tier 1 bosses can be defeated with early-game equipment. Their fights consist of three stages.
Rumia is the youkai of the dusk. She has 2,300 health (3,220 in Expert Mode). She can be summoned by using Meat of Questionable Origin at night. If she is not defeated by dawn (4:30 am), she will despawn.
Tier 2 bosses should be tackled using late Pre-Hardmode equipment. Their fights consist of three stages.
Tier 3 bosses should be tackled using early Hardmode equipment. Their fights consist of four stages.
Medicine Melancholy is an abandoned doll that has come to life and gained the power to control all kinds of poisons. She has 15,600 health (23,400 in Expert Mode). She can be summoned by using Black Bile.
Tier 4 bosses are intended to be fought after the Mechanical Bosses. Their fights consist of four stages.
Tier 5 bosses are intended to be fought after Plantera. Their fights consist of five stages.
Tier 6 bosses are intended to be fought after the Golem. Their fights have six stages.
Tier 7 bosses are about as difficult as the Moon Lord. Their fights have seven stages.
Utsuho Reiuji is a hell raven who has attained the power to control nuclear fusion. She has 133,000 health (199,500 in Expert Mode). She can be summoned by using a Charged Solar Fragment near the Subterranean Sun. If no new world was generated for the playthrough (and the Subterranean Sun mini-biome does not exist), she can instead be summoned anywhere in the Underworld. She will not follow players out of the Underworld and will despawn instead.
Minibosses may be encountered at random while exploring the world. Unlike other bosses, they cannot be spawned at will.
Kisume is a tsurube-otoshi youkai, waiting to drop on unsuspecting prey from above. She has 1,500 health (2,100 in Expert Mode). Players may be ambushed by her upon triggering a trap in the underground.