Monstro is a slow-moving but hard-hitting boss commonly encountered early on in the game.
He will semi-randomly switch between hopping towards the player, spitting a bunch of blood shots (after smiling), or launch into the air and land at the spot the player was standing in when he went up along with blood shots fired in every direction when he hits the ground.
- The distance between Isaac and Monstro will not influence the attack he'll choose, he switches between them at will. Therefore, you'll want to stay at medium range to retain maximum flexibility. The blood shot spray looks nasty, but your shots can actually knock droplets out of the air, those with a high tear rate may choose to simply carve a safety zone out with sustained fire. Note: Spectral Tears seems to pass through the droplets without destroying them.
- It's also possible to circle around Monstro while staying at a short distance. This way, you don't have to worry about his shots, but his small leaps become a bit more dangerous.
- Despite his bulk, Monstro moves around a fair bit; area of effect items (like Mr. Boom, Lemon Mishap, or Doctor's Remote) will not be very effective unless you get lucky on placement. Doctor's Remote, however, works somewhat well as you can use mouse clicks to stay on target with Monstro.
- Regular bombs take large chunks out of his health, but if he decides to launch you may end up wasting the bomb. An easy way to use area of effect items is when Monstro makes a huge jump, he will land approximately at your last position before he jumped, so just use the item before moving.
- If you're down to one heart, avoiding damage becomes a number-one priority as some of his shots (the bigger ones) can deal up to a full heart of damage.
- For some people it's hard to tell where he is when jumping in the air, so homing shots can help to predict his landing.
- It's possible to run underneath Monstro while he is "hopping". This can make shooting a bit easier.
- Pay attention. If Monstro uses his blood spray while you are cornered, look for an opening. There's an opening in every barrage he throws at you, so use this to your advantage.
Much smaller and has less health. There will be multiple Monstros that you will have to battle simultaneously. In boss rooms, it's two and in normal rooms in later levels, one will be added to the amount that would spawn in the room by default. Obviously, when smaller, it's harder to stay still and maintain fire, and with two or three of them present, it's best to run in a circle around them and never fully stop moving unless they're both just hopping around.
Slightly larger and has more health. He can't launch himself into the air and uses his shot attacks more often.
- There is a bug with Monstro where if he kills you at point-blank range, he will go crazy with facial expressions until you explode.
- Using Mom's Pad whilst Monstro does his huge jump will cause him to float for the duration of the item's effect, and make him impossible to hit until the stun wears off.
- Also referred to as The Hairlip in the "Unholy Edition" art booklet
- Monstro possesses a cleft lip, or "harelip", a common birth defect.
- Monstro means Monster in Portuguese.
- Monstro appears in the demo.
- One of his teeth is missing, possibly referring to the item Monstro's Tooth, however said item is disabled when fighting him.
- Monstro's look is very similar to SnackOLantern, a main character of a mini-game by the same name posted by Edmund on newgrounds in 2003.
|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|