Tentacruel

Base stats: 80 hp, 70 atk, 65 def, 100 spd, 80 satk, 120 sdef

Abilities: Clear Body, Liquid Ooze

Resistances: fire, water, ice, steel, bug, poison, fighting
Weaknesses: ground, psychic, electric
No Immunities

Pros:
+ Great typing for a non-steel type (7 resistances to 3 weaknesses)
+ Two great abilities (clear body prevents stat reduction from both attacks and intimidate, liquid ooze stops seed stallers dead)
+ Second highest speed of any water type
+ Walls Surf / Ice Beam combination as well as most other special attacks quite easily
+ Has strong attacks available to gain STAB from both types
+ Decent move pool fills several roles
+ Mixed sweeping potential limits (but does not leave it completely free of) true counters

Cons:
- Relatively weak defense (KO'd by EQ from just about anything)
- Two special weaknesses prevent it from being a true special wall
- Attack stats are fairly low unsupported.
- Limited physical movepool generally prevents Swords Dance from giving it pure physical sweeping capability.

General counters: Blissey, Snorlax, and Regice if switched in immediately, otherwise SD sludgebomb gets 'em; Quagsire, Swampert, and Whiscash when you don't have gigadrain; most steel types (exceptions being Aggron and Steelix); Gyarados when you don't have HP electric, and possibly even when you do; anything with EQ that either is faster than or can take a hit from Tentacruel.

Movesets:

Tentacruel (M) @ Leftovers
Trait: Clear Body
EVs: 12 HP / 30 Atk / 216 Spd / 252 SAtk
Hasty Nature (+Spd, -Def)
- Hydro Pump / Surf
- Sludge Bomb
- Substitute / Ice Beam
- Swords Dance
By far the most commonly used Tentacruel set, and for good reason. Its mixed sweeping capability prevents it from being walled by pure special or pure physical walls. In UU, 319 spd (hasty + 216 evs) outspeeds Jynx and Houndoom among other 95 base speed pokemon. In UU, sub > Ice Beam due to the lack of dragons, which are the main reason Ice Beam is needed. Sub is also more useful in UU where status ailments such as t-wave, hypnosis (or sleep powder), and c-ray are more common. Sub also helps eliminate the need for prediction. Hydro Pump > Surf allows it to KO things such as Aggron, Steelix or, others that would otherwise KO Tentacruel with EQ after a surf (negating its relatively low special attack at the expense of a little accuracy). Even so, however, surf is always on there as an option for those who prefer to be able to count on a hit and just attack with the sub up before switching out. In OU, drop the speed to 300 (hasty + 148 evs) to outspeed adamant Salamence and other base 100 spd pokemon. Ice Beam > Sub deals with the dragons in OU, while sub can still be useful for prediction problems. 12 HP EVs in general for ideal lefties recovery. The spread between attack and special attack is up to the user, but after 2 or 3 swordsdances, I've found the attack is high enough for sludgebomb to handle most things hydropump can't, so I personally always just dump 252 into satk.

Tentacruel (M) @ Leftovers
Trait: Liquid Ooze
EVs: 12 HP / 252 Spd / 246 SAtk
Timid Nature (+Spd, -Atk) / Modest Nature (+SAtk, -Atk)
- Surf
- Ice Beam
- Giga Drain / Hidden Power [Electric]
- Substitute / Hidden Power [Electric]
The special sweeper set: not nearly as common or as devastatingly effective as the mixed sweeper, but it throws the most common counters for the above set for a loop. Giga Drain devastates Quagsire, which is by far the most common and generally accepted Tentacruel counter in UU. HP Electric gives it a weapon against Gyarados and Mantine, which would otherwise stop this set dead. The main problem with the set is that with its relatively low special attack, this set is easily walled by common special walls that the above set would dominate. In UU, one generally chooses speed over power simply because of the metagame, but if you want to increase its damage, you can always consider the modest nature. Also, as always in UU, there is the potential for adding a petaya berry to pinch sweep with. The other nice thing about this set is that with its reliance on special sweeping, you don't really need clear body for intimidate, so you can give it liquid ooze and let it be your seed-stall counter (though I suppose if you're not worried about indimidate, you can always do that with the other set).

Other options: Tentacruel has a number of other moves that can be useful. Confuse ray is always good to encourage a switch or buy time. Haze can be useful coupled with Tentacruel's limited special walling ability. Rapid spin deals with spikes and leech seed (if you don't have liquid ooze I suppose). Mirror coat is devastating when coupled with that sexy special defense. Barrier can be useful to give it general walling abilities. Even toxic can have its uses.

Final Analysis: Tentacruel is without a doubt one of the most dominant pokemon in the UU metagame, with its only true counter there being Quagsire (to the point where you rarely see a truly competative UU team without Quagsire). With one of the best speeds in the UU metagame and a sweeper set that can smoke 90% of pokemon after 2 or 3 swords dances, it can literally wipe entire teams off the map. That sexy special defense allows it a fairly easy setup against sweepers that rely on the type coverage of Surf and Ice Beam (which is the majority of water pokemon) and also allows it to withstand even STABed Thunderbolt and Psychic attacks.

Tentacruel is an awesome pokemon....

I've been thinking of a CB set. Sludge Bomb, HP Fight, Hydro Pump, something....With its speed and the CB can boost the attack stat from "meh" to "decent", I could serve as a nice "LOL" for the limited time people don't realize CB.

what about miror coat with it's high sp .def it can counter zam's psychic and raikou/zappy's t bolt and mirror coat them back

That was covered in the "other options" portion of the analysis. Thank you though.

oops sorry
tentacreul is one of my favs
what about barrier to make him a tank?

"Barrier can be useful to give it general walling abilities."

Yeah... already mentioned.

*grin* sometimes it amazes me on how much people know of certain info about specific pokemon, it makes me strive for more knowledge, Tentacruel is nice but I like Gyarados, an Starmie, more attack abilities like Starmie using Thunder, Gyarados using Flamethrower...etc

Non-stab Flamethrower on a low Sp. Atk Gyarados? Even if he did get STAB on Flamethrower, it's redundant.

Gyrados is more a physical sweeper. A guy a face on netbattle likes this moveset:

@leftovers

Yeah, only problem is Gyarados isn't UU.

Either way, I've seen people use it in UU's without any confrentaion.

As far as most are concerned you could throw a skarm on team and call it UU, just so long as you don't try to enter a UU tourny with it.