Sheer Force Kyurem: This would definitely be a bit overpowered as a wallbreaker, but I doubt it would be broken in general. Sheer Force Kyurem would have so much going for it, as the free 33% boost to Ice Beam, Focus Blast, Earth Power, and Flash Cannon definitely helps, and giving it a Life Orb is would make it so powerful at no cost. Despite the bad defensive typing, Kyurem does have a lot of bulk to take a hit, so a good deal of offensive Pokemon won't be able to break Kyurem before it breaks them. However, Kyurem-B's crappy defensive typing leaves it wide open to a lot of things, like Keldeo, Azumarill, Mega Charizard X, Mega Diancie, Mega Lopunny, Latios, Mega Gallade, Mega Gardevoir, and a bunch of other things, and having a Stealth Rock weakness can greatly effect its bulk. But just from the wallbreaker perspective, there are very few safe switches to this monstrosity, and not that many defensive Pokemon can take attacks that powerful. Kyurem might break defensive cores, but I doubt it'll be broken as a whole. This is a bit of a daring Theorymon, but I don't think it would be too much for OU to handle.
Reflect Type Jellicent: I see where this is coming from, but it just wouldn't work out at all. Jellicent is way too slow to properly use Reflect Type, as it's almost always going to get hit before changing its type. The reason why Reflect Type Starmie and Latias work is because of their good Speed tiers that allow them to change type before getting hit, but Jellicent lacks that Speed, so it would only get the chance to change its type on either uninvested base 60's or attackers that don't have an easy time against Jellicent anyways. Jellicent would also have to give up a moveslot to use Reflect Type, with three of those moveslots being mandatory for Scald, Recover, and either Toxic or Will-O-Wisp, so you'd be giving up on Ice Beam or Taunt, both of which have important uses. Good effort, but I gotta say no.
Electric/Steel Flash Cannon Rotom-F: Now this is a pretty cool Theorymon, breaking ground as the first Theorymon to get two changes and whatnot (at least the first I've seen before). With the new Steel typing and Levitate actually being useful now, Rotom-F now boasts 11 resistances and two immunities, including coveted paralysis and Toxic immunities, as well as a very nifty Stealth Rock resistance. Mega Diancie, non-Superpower Landorus-T, Latios, Thundurus, Sand Rush Excadrill, Diggersby, regular Gyarados, Mamoswine, Mega Beedrill, and Dragonite are all beaten by Rotom-F, so you know that this thing has some defensive prowess. Sure, Mold Breakers and users of Fighting- and Fire-type moves can slip past Rotom-F more easily now, but gaining a crap-ton of resistances, an extra immunity, a Stealth Rock resistance, and two status immunities REALLY outweights any of its flaws. Definitely getting my vote.
Quiver Dance Galvantula: I wanted this to work, I really wanted this to work. Sadly, the more I look at this, the less I think it'll succeed as a Theorymon. With Quiver Dance, Galvantula could be a powerful sweeper in theory, as 91% accurate Thunders are pretty powerful, especially if they get a Quiver Dance boost, and a +1 sweeper with 108 base Speed can be pretty hard to revenge kill outside of Talonflame, Choice Scarf, and weather sweepers. Galvantula could threaten Keldeo, Gengar, Mega Gyarados, non-Choice Scarf Latios, Mega Aerodactyl, and Tornadus-T after a single Quiver Dance boost, so it's got the sweeper part down. But I'd honestly rather just use Volcarona as a Quiver Dance sweeper, simply because Volcarona has significantly more power, visibly better bulk, a better STAB attack in Fiery Dance to consistently gain power even when not using Quiver Dance, and recovery in Roost. Sure, Galvantula has a paralysis immunity and lacks a 4x Stelth Rock weakness, but it still has a 2x Stealth Rock weakness, and its horrific bulk means that any hit will be fatal anyways, so getting the chance to set up requires more support and planning than it's worth. I just pray that we get that one buff to Galvantula that can let it shine. One day.