Kay, here to answer some more theories.
What if Entei got Swords Dance?
This would be pretty cool, and this means Entei could easily run Flame Plate+SD if you want freedom over moves, and Entei could do an admirable job at wallbreaking except without immediate power; Entei could also use buffed ExtremeSpeed to sweep faster teams with its +2 Priority move that hits hard coming off of Entei; kinda like Absol in a way. This would be a really cool tool to give Entei more freedom of moves while still giving it a lot of power to use; it also allows it to step away from the standard CB set sometimes. (and besides, this would definitely be legal with Flare Blitz+Espeed, Swords Dance is a TM!)
What if Entei got Power Whip?
If it did, I can see Entei running this over HP Grass all the time, as this now gives Entei a powerful and reliable weapon against incoming Kabutops, Omastar, and Rhydon; three Pokemon that typically stop Entei from nuking teams into pieces. It also has a nice tool to handle other Water-types such as Slowking, Lanturn, and to a lesser extent Quagsire, and overall just gives Entei more overall coverage. This would definitely be a good tool for Entei to have, despite not making any flavor sense at all.
What if Quagsire got Stealth Rock?
I'll tell you this; Quagsire would be so much better if it got Stealth Rock, and I think it would be a staple of teams if it got the move. Quagsire, although rather outclassed, has a niche, and a very good one; Unaware is a great ability and allows Quagsire to stop cold setup sweepers such as BU Gallade, Durant, Absol, and a bunch of others. It also has reliable recovery in Recover allowing it to be effective, but even then, it still finds itself outclassed by the likes of Poliwrath, Alomomola, and others. But with SR, however, I think Quagsire can fill its niche effectively, but have the edge now over other Waters not only because of Unaware+Recover, but its ability to support the team with Stealth Rock. Not I'll tell you; SR is one of the best moves in the game, and Quagsire being able to do this would make it a milestone better because now it has a way to really support its team. I'd say Quagsire would be pretty good in RU if it got this move (although I'll admit I've used Quag successfully before).
What if Cryogonal got Volt Switch?
Thinking about it now, this would give Cryogonal another role outside of spinning. Although this wouldn't mean much for Cryogonal as far as spinning goes; because it's weak to SR and is super vulnerable to Pursuit, so as a spinner, Cryogonal would not get much out of Volt Switch in its spinning roles. However, Celever hit it head on with what Cryogonal could get from Volt Switch. Cryogonal would be a pretty good Dual Screens user, being able to set up both screens for the team, but also provide support with Switching out to something quickly to grab momentum. Cryogonal could also hit Water-types decently hard while serving as a scout. Cryogonal could definitely find some new roles with this move.
What if Entei learned Wild Charge?
This would be pretty swell, as Entei could definitely find a lot of use for this move because Fire+Electric is good coverage. Entei can use a great coverage move now to handle Slowking and friends with more ease, and also prevents Entei from being setup fodder for Omastar, which can be costly if that thing gets hazards or gets a boost, and you can probably lose. This would be pretty cool imo.
What if Ambipom was RU?
Unfortunately, I think this wouldn't do much, if anything. Ambipom is horribly outclassed by the likes of Cinccino, who has high Speed, but also has much more power and has the ability to eliminate Smeargle, Snover, etc as well, which eliminates the one niche Ambipom could possibly fill. Cinccino has more power, so it has much better sweeping chances than Ambipom, while Cinccino has the luxury of having the valuable ability to break Substitutes. Bullet Seed means it handles Kabutops and Omastar, better, and also prevents Omastar from boosting. The bulky nature of the RU metagame does not help Ambipom's case either; as it gets beaten as it is so frail it can't take a hit; but it also can't do a significant amount of damage back. Sad thing is, even if Ambipom has more power, there simply isn't much it could do in RU. It will probably have no impact outside of the initial hype at the beginning.
Anyways, as for a theorymon of my own:
What if Scolipede learned Stealth Rock?
I know this doesn't make any flavor sense, but hey, we've had some Pokemon that don't seem like they could learn SR actually learn the move (Infernape, Mesprit, Druddigon). Scolipede learns Spikes and Toxic Spikes, and has amazing speed to be a hazards lead. How would this affect Scolipede's performance in the tier? Will it be able to push Scolipede back into his rightful tiering placement?
I said this before, but anyways, how would this do?