Molten Freddy is an animatronic consisting mostly of wiring similar to Ennard from Sister Location, his body disfigured with protruding wires. He possesses no suit, wearing the decayed Funtime Freddy's mask with sharp teeth, blood splatters around the mouth, the faceplates seem to be melted and a rusty brown top hat and bow tie. There are hanging wires that run along the body of Freddy and are shaped differently from the other animatronics, which possesses wires coiled to look like muscle tissue, while Ennard's wires are tangled mess. He seems to have two arms, and a torso in his jumpscare, with the rest of him being a pile of wires as seen in the alley.
Several eyes from his body are the eyes of other animatronics. The eyes on Molten Freddy's body are similar to the pixelated version of Ennard, in which the player himself (Michael) regurgitates Ennard into the sewer.
A yellowish-orange eye belongs to Funtime Foxy.
A magenta eye belongs to Bon-Bon.
A sapphire blue eye belongs to Funtime Freddy.
A purple eye belongs to Ballora.
Five Nights at Freddy's: Sister Location (As Funtime Freddy and Ennard.)
Ultimate Custom Night
He also appears with Ennard too.
He also climbs in the vent system, but is much faster than the other animatronics when it comes to maneuvering his way toward you. You can track him on the vent monitor and can hear his laugh when he is poised to attack. Close the vent door on him to send him away.
— Molten Freddy's Ultimate Custom Night Description
Molten Freddy will climb through the vents making his way towards the player's office. He can be tracked on the vent monitor along with the other vent animatronics excluding Ennard. The player can't use the vent snare to stop him from reaching the vent opening, but instead, closing the vent door when Molten Freddy will laugh crazily. However, if the player hears Molten Freddy's laugh and does not close the vent door in time, they will be jumpscared by him, resulting in a Game Over.
The following information contains spoilers. To view them, click the [show] tag.
One bi-i-i-ig, happy family!
Thanks for letting me join the pa-arty, I-I'll try no-o-ot to disappoint.
Knock-kno-o-o-ock, I-I-I-I'm heeeeeere!~
Oh, what a p-pleasant surprise!
Molten Freddy's laughs when in the vents.
Molten Freddy's jumpscare sound, this is shared with the rest of the animatronics who attack you.
Molten Freddy is salvaged on the first night and is worth $500.
If the player buys the Discount Ball Pit on Monday, he is replaced by Lefty's wooden sign, hinting that he is hiding inside the Discount Ball Pit.
There exists a picture of Molten Freddy sitting in an alley, which appears to be his rare death screen which points to him actually being Ennard as it is just a mask on a tangle of wires and endoskeleton parts.
Although Molten Freddy's mask bears some resemblance to Funtime Freddy's, several things are different, such as: Him having no blush, accents having molten brown texture instead of a shiny mauve purple texture, his hat doesn't have a stripe, lighter color on jaw and etc, pointing to it being a different mask.
It's unknown where he got it from.
There is a blueprint of Molten Freddy's mask which can be found in the Insanity Ending.
Molten Freddy's eye surprisingly changes color.
Yellow for the Rare Death Screen and for it's Custom Night Icon
Orange for Salvage attack
Red for the Office attack
However, this oddity may be the cause of lighting effects.
This may also be caused by the presence of three different spirits within Molten Freddy (Those possibly of Funtime Freddy, Funtime Foxy and Ballora).
Molten Freddy's laughs are reused in Ultimate Custom Night.
Kellen confirmed in a Q&A with Dawko that Molten Freddy had scrapped lines, but he cannot share them with the public currently.
Kellen also confirmed that he voiced Molten Freddy's lines on November 8th, 2017.
Molten Freddy is one of the few animatronics to climb into the center vent in UCN, others being Mangle, Withered Chica, Springtrap (FNaF 3), and Ennard.
In UCN, once Molten Freddy is in front of the vent in the office, in which he will laugh, there is sometimes an occurrence where he does it twice, which the player needs to close the vent twice.
This has since been fixed as of Version 1.024.
Molten Freddy in the Salvage Room, Passive. (First Phase)
Molten Freddy staring at the player, Agitated. (Second Phase)
Molten Freddy, preparing to attack in the Salvage Room, Hostile. (Third Phase)
Molten Freddy's jumpscare in the Salvage Room.
Molten Freddy's past jumpscare from the office.
Molten Freddy's current jumpscare from the office.
Molten Freddy's last frame of jumpscare in the Salvage Room.
Molten Freddy's last frame of its jumpscare when attacking the player in the Office, transparent background.
Molten Freddy in the alley.
Molten Freddy in the alley but lightning flashes.
Molten Freddy burning in the Completion Ending.
Molten Freddy's blueprint, from the Insanity Ending.