Two central antagonists with big smiles from indie games based off of/inspired by a popular video game franchise (Earthbound/Mother and Five Nights at Freddy's) who at first don't seem like much, simply appearing as a living inanimate object with a face, but later on it is revealed that they have truly murderous and sadistic intentions. They have similar reality-warping powers and 4th-wall breaking abilities, and are aware that they are in a game, to which they eventually toy around with in their final encounters (Flowey messes around with the SAVE/LOAD function in Undertale and Flumpty messes around with some of mechanics in the game like the Temperature Bar, the Exposure Bar, the Power Bar, etc. in ONAF 3, specifically in Flumpty Night). Aside from their reality-warping abilities, both have a few similar abilities, most importantly their abilities to shapeshift and contert their faces, overall showing their truer nature. They have little to no problem killing or torturing the people they call friends or family, who consist of the rest of the cast (Flumpty has been shown to somewhat torment Blam in the One Week At Flumpty's videos, and he just straight up kills his entire gang in ONAF 3, while Flowey has no problem killing Asgore, his father, in the Neutral Route, and everyone in the Pacisfist Route, including his parents Toriel and Asgore), and are known for "befriending" the protagonist of their story, who they actually go out of their way to kill (Despite calling you his "best friend", Flumpty still goes out of his way to kill the protagonist of ONAF, and despite supposedly trying to befriend Frisk in the beggining and referring to them as his friend or pal, he constantly tries to kill them during the game's events). But inspite all of this, they surprisingly don't seem to be all that evil (Flowey is a bit sympathetic and he only really is evil because he lacks a soul, he sorta redeems himself at the end of the Pacifist Route when he turns back into Asriel, and is a bigger pushover in the Genocide Route, and while Flumpty isn't really sympathetic, he's an ernest and fair villain via giving the player a chance to beat his game, often by limiting his powers, and even lefts them off the hook once they survive his game). Both also have a similar introductory line ("Howdy! I'm Flowey! Flowey the Flower!"/"Hi! I'm Flumpty Bumpty! I'm an egg."), seemingly have knowledge of other universes (Flowey seemingly knows about the alternate timelines in the Undertale universe (or Multiverse, I guess?) and possibly creating some of his own, and Flumpty can just outright travel to different fictional stories, explaining where he got the corpses of Winnie the Pooh, Piglet, Smiley, Freddy Fazbear, etc.), LOVE to kill (which probably should've been noted earlier), and strangely their games have similar themes of time and time repeating, which they are somewhat involved with (Undertale's whole SAVE/LOAD shenanigans, which is a power Flowey has, and ONAF with it's night system and how all the games were set on the same night which Flumpty was responsible for)

Oh, and I guess their names start with "FL".

I still prefer Bill vs Flumpty and Dimentio vs Flowey, but DAYUM this is good!