Gemini are a set of conjoined twins (parasitic twins) attached by an umbilical cord.
The larger of the two will run after the player fairly quickly, but after a while, he runs out of breath and has to stop. The smaller one drifts along and will fire fast-moving blood drops at the player if they come near. The umbilical cord acts like an elastic tether, keeping them in roughly the same area while not much restricting range of movement.
If you kill the larger one, the smaller one will become enraged, abandoning ranged attacks in favor of charging at the player. If you deliberately focus-fire the small one from the start, it will be killed and you only have to focus on the big one. This can be tricky, as you have to shoot around the larger one. The best time to do this is when he stops to catch his breath. Watch out for the little one's shots when trying this. The small one has little weight, and can be shoved around with rapid-fire much like the flies. Even at normal speeds, a sustained volley will keep him bouncing in place for several seconds at a time if the player has sufficient knockback.
Your best option for handling these two is to run around the edges of the room, firing behind you as you go. Gemini's room will often have two L-shaped patches of rubble separating the center from the edges; you can use these ridges to keep the larger twin from cutting across the middle.
Movement-controlling items like Mom's Bra and Mom's Pad can be helpful if you find yourself unable to stay ahead of the larger twin's frequent charges. Aimed burst damage items like Bob's Rotten Head and Shoop Da Whoop can also help, but be sure you have some distance before you use them. Bombs or Mr. Boom can be used during the brief pauses for breath, but your timing will have to be impeccable.
Gemini starts off with the two detached; however, the smaller one will act as normal. If enraged by the death of the larger one, it does not move as fast as the normal one. However, there is a chance where just the smaller half of him is green. In this case, it's easier on the player, as when it starts its charge, it'll move slower towards the player and is much less of a threat.
Gemini starts out with increased health, but decreased speed, which is more noticeable if the larger twin is coloured. This actually makes Gemini easier, though it takes longer to defeat. As with the Green Champion, there is a slight chance of only the small twin becoming blue, resolving in the older one acting normally, but the smaller twin moving very slowly. Both twins' overall health is increased.
- Two pairs of Gemini can also be found in normal rooms of The Womb and Sheol, not rarely with one or even both pairs in a Champion Form.
- Gemini will occasionally be replaced by Steven after you complete The Basement 25 times.
- Gemini is named after the starsign by the same name, symbolised by the twins.
- Gemini appears in the demo.
- If you have Mom's Contacts and Chocolate Milk while fighting Gemini, there is a chance that the smaller sibling will still behave as if the larger one is there if you kill the larger one first.
- Gemini are also known as simply The Twins according to the "Unholy Edition" art booklet. Their individual names are given as Suture and Contusion, with the larger one presumably being Suture (note the sewn-on patch of skin on his head) and the smaller one therefore being Contusion.
- Their names stem from a cut boss concept (similar to that of Gemini) of Gish, another game from Edmund McMillen.
|Basement||Larry Jr. • Monstro • The Duke of Flies • Gemini • Steven • Famine|
|Cellar||Widow • Pin • The Duke of Flies • Famine • Gurdy Jr. • The Blighted Ovum|
|The Caves||Fistula • Peep • Gurdy • Chub • C.H.A.D. • Pestilence|
|Catacombs||The Husk • The Hollow • The Blighted Ovum • The Carrion Queen • Peep • Pestilence • The Wretched • Gurdy Jr.|
|The Depths||Loki • Monstro II • Gish • War • Mom|
|Necropolis||Mask of Infamy • Daddy Long Legs • The Carrion Queen • The Bloat • Loki • War • The Wretched • Mom|
|The Womb||Scolex • Blastocyst • The Bloat • Death • Conquest • Daddy Long Legs • Triachnid • Teratoma • Mom's Heart • It Lives|
|Utero||Teratoma • The Bloat • Death • Conquest • Daddy Long Legs • Triachnid • Lokii • Mom's Heart • It Lives|
|Sheol||The Fallen • Satan|
|First to fifth and seventh level||The Fallen • Headless Horseman|