Base stats:
80 HP
70 Atk
65 Def
80 SpAtk
120 SpDef
100 Speed
Abilities:
Clear Body: Prevents the enemy from lowering this Pokémon's stats.
Liquid Ooze: Leeching moves cause the enemy to lose HP instead.
Rain Dish: Heals 1/16 max HP in rain.
Moves via level up:
Poison Sting
Supersonic
Constrict
Acid
Toxic Spikes
BubbleBeam
Wrap
Acid Spray
Barrier
Water Pulse
Poison Jab
Screech
Hex
Hydro Pump
Sludge Wave
Wring Out
Supersonic
Constrict
Acid
Toxic Spikes
BubbleBeam
Wrap
Acid Spray
Barrier
Water Pulse
Poison Jab
Screech
Hex
Hydro Pump
Sludge Wave
Wring Out
Moves via TM/HM: (Gen. 5)
TM06 Toxic
TM07 Hail
TM09 Venoshock
TM10 Hidden Power
TM13 Ice Beam
TM14 Blizzard
TM15 Hyper Beam
TM17 Protect
TM18 Rain Dance
TM20 Safeguard
TM21 Frustration
TM27 Return
TM32 Double Team
TM34 Sludge Wave
TM36 Sludge Bomb
TM42 Facade
TM44 Rest
TM45 Attract
TM46 Thief
TM48 Round
TM55 Scald
TM66 Payback
TM68 Giga Impact
TM75 Swords Dance
TM84 Poison Jab
TM87 Swagger
TM90 Substitute
HM01 Cut
HM03 Surf
HM05 Waterfall
HM06 Dive
TM07 Hail
TM09 Venoshock
TM10 Hidden Power
TM13 Ice Beam
TM14 Blizzard
TM15 Hyper Beam
TM17 Protect
TM18 Rain Dance
TM20 Safeguard
TM21 Frustration
TM27 Return
TM32 Double Team
TM34 Sludge Wave
TM36 Sludge Bomb
TM42 Facade
TM44 Rest
TM45 Attract
TM46 Thief
TM48 Round
TM55 Scald
TM66 Payback
TM68 Giga Impact
TM75 Swords Dance
TM84 Poison Jab
TM87 Swagger
TM90 Substitute
HM01 Cut
HM03 Surf
HM05 Waterfall
HM06 Dive
Moves via TM: (Gen. 4)
TM03 Water Pulse
TM06 Toxic
TM07 Hail
TM10 Hidden Power
TM13 Ice Beam
TM14 Blizzard
TM15 Hyper Beam
TM17 Protect
TM18 Rain Dance
TM19 Giga Drain
TM21 Frustration
TM27 Return
TM32 Double Team
TM36 Sludge Bomb
TM42 Facade
TM43 Secret Power
TM44 Rest
TM45 Attract
TM46 Thief
TM55 Brine
TM58 Endure
TM66 Payback
TM68 Giga Impact
TM75 Swords Dance
TM78 Captivate
TM82 Sleep Talk
TM83 Natural Gift
TM84 Poison Jab
TM87 Swagger
TM90 Substitute
TM06 Toxic
TM07 Hail
TM10 Hidden Power
TM13 Ice Beam
TM14 Blizzard
TM15 Hyper Beam
TM17 Protect
TM18 Rain Dance
TM19 Giga Drain
TM21 Frustration
TM27 Return
TM32 Double Team
TM36 Sludge Bomb
TM42 Facade
TM43 Secret Power
TM44 Rest
TM45 Attract
TM46 Thief
TM55 Brine
TM58 Endure
TM66 Payback
TM68 Giga Impact
TM75 Swords Dance
TM78 Captivate
TM82 Sleep Talk
TM83 Natural Gift
TM84 Poison Jab
TM87 Swagger
TM90 Substitute
Moves via breeding
Acupressure
Aurora Beam
Aqua Ring
Bubble
Confuse Ray
Haze
Knock Off
Mirror Coat
Muddy Water
Rapid Spin
Tickle
Aurora Beam
Aqua Ring
Bubble
Confuse Ray
Haze
Knock Off
Mirror Coat
Muddy Water
Rapid Spin
Tickle
Moves via tutor: (Gen. 4)
Dive
Icy Wind
Knock Off
Role Play
Snore
Icy Wind
Knock Off
Role Play
Snore
Moves via tutor: (Gen. 3)
Double-Edge
Endure
Icy Wind
Mimic
Sleep Talk
Snore
Substitute
Swagger
Swords Dance
Endure
Icy Wind
Mimic
Sleep Talk
Snore
Substitute
Swagger
Swords Dance
Dream World Exclusive Moves:
Giga Drain
GBU Singles Sets:
Acid Spray
Item: Wise Glasses/Expert Belt/Leftovers/Black Sludge
Ability: Liquid Ooze/Rain Dish
Nature: Modest
EVs: 252 SpDef/252 SpAtk/4 HP
Moveset:
-Acid Spray
-Giga Drain
-Surf
-Hidden Power Fire/Ice Beam
Acid Spray will be your main STAB. Pitifully weak at first, in it's own way, gives a boost to Tentacruel's only mediocre base 80 SpAtk stat, since it lowers your opponents Poke's SpDef stat by two stages every time, while still dealing some damage.
Giga Drain gets the second slot. With it's buff to 75 base power in Gen 5, it is now competitively viable. Coupled with Acid Spray's SpDef drop, the HP gain can be a huge difference maker, and potentially KO some slower Ground types that threaten your Poison typing.
Surf gets slot three for a second, and more powerful STAB option. Don't bother wasting damage output trying to either inflict burn with Scald, or risking a miss with Hydro Pump.
Fourth move slot depends on Tentacruel's team mates. Outside of rain teams, HP Fire gets the main slash, along side of Liquid Ooze ability, and either Expert Belt or Wise Glasses for it's hold item. This is to deal with Steel types that will otherwise wall you. With Expert Belt's and Wise Glass' boost, you will OHKO Scizor after Stealth Rock damage if it thinks it can set up on you. It also provides 2HKO's on Skarmory, Forretress, and Ferrothorn.
On a rain team, HP Fire will be rendered useless. Since a rain boosted Surf will hit Steels for decent damage still, Ice Beam should be used to hit Dragons harder. Also in the rain, Rain Dish ability and either Leftovers or Black Sludge should be used for even more survivalbility.
Additional comments:
This Tentacruel variant fairs just as well under sunny skies as it does in the rain. With the combination of the sun, and Acid Spray, HP Fire can hit scary hard if Acid Spray's SpDef drop has first been applied. Giga Drain can hit three of the four weather changers (Tyranitar, Hippowdon, and Politoed) for super effective damage, while both Acid Spray and HP Fire hits Abomasnow super effective. In addition, Tentacruel's Water/Poison typing can help repel other Pokemon that would target sun teams by defending versus Grass type Chlorophyl Pokes on opposing sun teams, and other Water types (especially Drizzletoed, since it can change your weather) that may try to resist and KO your Fire types. However, the sun will weaken Surf's power too much. Ice Beam, Knock Off, or Haze, can replace Surf just fine without loosing any of this sets other merits.
GBU Doubles:
To be announced...
GBU Triples:
To be announced...
GBU Rotational:
To be announced...
*I'll be editing/adding more sets to the OP as they are suggested*