Forge is a vampire who can rust things. His power, while unconventional, is very useful, especially in the hands of a writer like Araki. (Asspulls or not, he is still much better than me)
Forge could beat some characters, but not all of them. Who would get the short end of the stick and who could beat him?
Can: Caesar Zeppeli
This expert Hamon user nearly beat a Pillar Man, he can handle a vampire for sure. His Hamon also relies on bubbles that don't rust, so he would defeat Forge with little trouble.
Can't: Rudolph von Stroheim
Stroheim can beat a vampire due to German Science, as his bullets are faster than their recovery. However, even they have their limits. Also, he completely relies on metal, so Forge would be his biggest weakness, as he could rust him.
Can: Esidisi
Forge is for sure one of the best vampiric fighters, but he is not in the level of the Pillar Men. Esidisi is superior to Forge in every way, and attacks with his boiling blood. While Forge could try rusting the iron in the blood, it will be too hot for him to touch.
Can't: Mariah
Mariah's power is to make the target magnetic to everything, even large trucks. However, as Forge can rust whatever he touches and has vampiric reflexes and endurance, Mariah can't even scratch him.
Can: Joseph Joestar
Sure, Joseph will struggle and have to fight with one arm for the whole battle. His metal one is as good as gone. However, he will be smart enough to shield it and himself with Hamon, or use a rope full of it, or something else that isn't metal. His brains are the reason he can win against Forge, despite Forge being a genuine threat.
Can't: Risotto Nero
Risotto Nero has awesome abilities. Abilities that could obliterate most fighters. Forge isn't most fighters in this case. Risotto can create razors out of anything, even Forge's own body. However, Forge is a vampire, so he can survive the razors long enough to rust them and make them all useless. Risotto can turn invisible, but vampires have enhanced senses, so Forge can feel him. In short, Risotto is powerful, but against a vampire who rusts, he is really unlucky.
Can: Avdol
Avdol has fires strong enough to melt metal and rock, and vampires are really flammable. Also, Avdol doesn't rely on anything metal, just his Stand, which is really good for Forge.
Can't: Guido Mista
Mista is a badass, and his homing bullets are often successful. However, even if Forge couldn't just rust his gun or fire needles of rust, he is a vampire, so bullets will... stun him for a few seconds before he brings the pain. Mista is valiant, but stands no chance.
Can: Vanilla Ice
It's a battle against vampires, and Vanilla Ice has a Stand way above Forge's gift. Rust might be powerful, but it's nothing like a void that destroys with a touch, leaving nothing behind.
Can't: J.Geil
J.Geil might be very fast with his Hanged Man Stand, but the rapist is not getting away from this vampire. Good luck hiding in mirrors when Forge can rust every single one of them and make them useless. J.Geil can also try to stab him in the back with a knife. It will do wonders to vampiric skin, and certainly be more effective after getting completely rusty. Just kidding, J.Geil is boned.
Forge could beat some characters, but not all of them. Who would get the short end of the stick and who could beat him?
Can: Caesar Zeppeli
This expert Hamon user nearly beat a Pillar Man, he can handle a vampire for sure. His Hamon also relies on bubbles that don't rust, so he would defeat Forge with little trouble.
Can't: Rudolph von Stroheim
Stroheim can beat a vampire due to German Science, as his bullets are faster than their recovery. However, even they have their limits. Also, he completely relies on metal, so Forge would be his biggest weakness, as he could rust him.
Can: Esidisi
Forge is for sure one of the best vampiric fighters, but he is not in the level of the Pillar Men. Esidisi is superior to Forge in every way, and attacks with his boiling blood. While Forge could try rusting the iron in the blood, it will be too hot for him to touch.
Can't: Mariah
Mariah's power is to make the target magnetic to everything, even large trucks. However, as Forge can rust whatever he touches and has vampiric reflexes and endurance, Mariah can't even scratch him.
Can: Joseph Joestar
Sure, Joseph will struggle and have to fight with one arm for the whole battle. His metal one is as good as gone. However, he will be smart enough to shield it and himself with Hamon, or use a rope full of it, or something else that isn't metal. His brains are the reason he can win against Forge, despite Forge being a genuine threat.
Can't: Risotto Nero
Risotto Nero has awesome abilities. Abilities that could obliterate most fighters. Forge isn't most fighters in this case. Risotto can create razors out of anything, even Forge's own body. However, Forge is a vampire, so he can survive the razors long enough to rust them and make them all useless. Risotto can turn invisible, but vampires have enhanced senses, so Forge can feel him. In short, Risotto is powerful, but against a vampire who rusts, he is really unlucky.
Can: Avdol
Avdol has fires strong enough to melt metal and rock, and vampires are really flammable. Also, Avdol doesn't rely on anything metal, just his Stand, which is really good for Forge.
Can't: Guido Mista
Mista is a badass, and his homing bullets are often successful. However, even if Forge couldn't just rust his gun or fire needles of rust, he is a vampire, so bullets will... stun him for a few seconds before he brings the pain. Mista is valiant, but stands no chance.
Can: Vanilla Ice
It's a battle against vampires, and Vanilla Ice has a Stand way above Forge's gift. Rust might be powerful, but it's nothing like a void that destroys with a touch, leaving nothing behind.
Can't: J.Geil
J.Geil might be very fast with his Hanged Man Stand, but the rapist is not getting away from this vampire. Good luck hiding in mirrors when Forge can rust every single one of them and make them useless. J.Geil can also try to stab him in the back with a knife. It will do wonders to vampiric skin, and certainly be more effective after getting completely rusty. Just kidding, J.Geil is boned.