Code:
Pokemon
Scyther
Sneasel
Yanma
Items
Berry Juice
This is what I feel the initial list should look like (pretty much Vader's banlist #4 but removing Tangela).
Scyther: What other people have said. Scyther reaches an absurdly high 22 speed, which coupled with 20 attack, Swords Dance, and Technician moves such as STAB Aerial Ace, STAB Bug Bite (also helpful for stealing Oran Berries), and a boosted Quick Attack. Scyther is an ridiculously powerful, dealing
at least 66.67% to an Impish max/max Munchlax, while a max attack Munchlax does 60.87-78.26% to min/min Scyther with Fire Punch. If Scyther gets one turn to set up, he can OHKO virtually everything in the metagame.
Sneasel: Also what other people have said. Sneasel is, coincidentally, one of the only (or maybe the only) pokemon that can revenge-kill Scyther, as Sneasel reaches 23 speed and can use priority Ice Shard. While Sneasel's 95 attack isn't as strong as Scyther's 105, 19 attack is still pretty threatening, especially when NOTHING outspeeds it. He also gets Swords Dance, which allows him to run a similar set to Scyther, replacing QA with IS and replacing his STABs to Sneasel's STABs.
Yanma: Hey look, another speedy pokemon. Yanma reaches 20 speed, enough to tie with the fastest valid pokemon in 5th generation; one Protect later, Yanma outspeeds all pokemon bar Choice Scarfed Scyther, Sneasel, Diglett, Elekid, and Voltorb. 17 Attack is good, especially with STAB Bug Buzz. Yanma also gets the buffed Giga Drain to heal itself if it gets tired sweeping.
Berry Juice: Last generation, Berry Juice was quickly banned. It heals a ridiculous 20 HP, allowing most pokemon to restore themselves to full health. It's the equivalent of having a "Max Potion Berry" in OU. This generation has given us a lot more defensive pokemon; take Nattorei's pre-evo as an example. 44/91/86 defenses are nothing to scoff at; with investment, Tesshiido reaches 24 HP, 17 Def., and 18 Sp.Def. With BJ activating at 6 HP, it would immediately heal Tesshiido to full health, leaving you to have to get through its sturdy defenses once more. With Berry Juice, you essentially have to fight the same pokemon twice.
I don't feel that Tangela should be banned right away as the only way it actually threatens the metagame is under Sun. With the advent of Sandstorm teams and pokemon such as Mogoyruu and Meguroko, I doubt Sun will thrive.
EDIT:
SupremeDirt said:
I could see an argument for allowing it but having item clause, but it's just too potent an option.
amphouse said:
Nothing banned, but how about an item clause?
IMO Item Clause would take away from the feel of Little Cup. With a limit to the items, stall wouldn't be rational (only one Oran user and one BJ user if BJ were to be allowed), and Hyper Offense wouldn't be either (1 Life Orb, 1 Expert Belt, 1 Choice Scarf). Little Cup just doesn't have the variety of viable items OU does.