I've been testing with this and I've received great results.
Chum Bucket (Tangrowth) (M) @ Choice Specs
Ability: Regenerator
EVs: 248 HP / 8 Def / 252 SpA
Modest Nature
- Leaf Storm
- Hidden Power [Fire]
- Focus Blast/Knock Off
- Ancient Power
I believe a choice specs Tangrowth set is a standard set in RU. That said, I've never played RU. Anyways, this thing is a great lure for many offensive and defensive pokemon alike. With a Leaf Storm backed up by a 100 base special attack stat and Choice Specs, it hits anything that doesn't resist it pretty hard. To put it simply, this thing is a nuke. Leaf Storm works well especially with Regenerator as you will be switching out a lot. With 248 HP investment, Tangrowth is pretty bulky and can survive a super effective non-STAB physical attack and retaliate with a strong move of your own.
Hidden Power is crucial to this set, and makes this thing a lure in the first place. Many counters and checks to Tangrowth are bulky grass types, such as Gourgiest Super and Ferrothorn, that can absorb leech seed and powder moves. Hidden Power DESTROYS these pokemon,nearly OHKOing Ferrothorn without any prior damage. Hidden Power Fire also allows Tangrowth to check bug type switch ins that could otherwise set up on Tangrowth, such as Mega Scizor. Skarmory, a pokemon that would usually find itself setting hazards up on Tangrowth, is 2HKOd.
Focus Blast is used to check Heatran switch-ins, nearly OHKOing it with stealth rock on the field. Knock Off is an alternative if you want to be able to check Latis and Chansey switch-ins, and can also be used to try to make your opponent think you are a defensive set.
Ancient Power is in the final slot as it allows Tangrowth to nail Charizard and Talonflame switch-ins. In general, Ancient Power is there to hit flying types that resist Focus Blast and Leaf Storm.
RELEVANT CALCS:
252+ SpA Choice Specs Tangrowth Focus Blast vs. 248 HP / 192+ SpD Heatran: 278-328 (72.2 - 85.1%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Tangrowth Hidden Power Fire vs. 252 HP / 4 SpD Gourgeist-Super: 242-286 (64.7 - 76.4%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Tangrowth Hidden Power Fire vs. 252 HP / 168 SpD Ferrothorn: 292-348 (82.9 - 98.8%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Tangrowth Hidden Power Fire vs. 252 HP / 0 SpD Mega Scizor: 384-456 (111.6 - 132.5%) -- guaranteed OHKO
252+ SpA Choice Specs Tangrowth Hidden Power Fire vs. 252 HP / 0 SpD Skarmory: 258-304 (77.2 - 91%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Tangrowth Ancient Power vs. 0 HP / 4 SpD Mega Pinsir: 416-492 (153.5 - 181.5%) -- guaranteed OHKO
252+ SpA Choice Specs Tangrowth Ancient Power vs. 0 HP / 0 SpD Mega Charizard Y: 340-404 (114.4 - 136%) -- guaranteed OHKO
252+ SpA Choice Specs Tangrowth Ancient Power vs. 0 HP / 0 SpD Mega Charizard X: 220-260 (74 - 87.5%) -- guaranteed 2HKO
252+ SpA Choice Specs Tangrowth Leaf Storm vs. 252 HP / 0 SpD Mega Sableye: 276-325 (90.7 - 106.9%) -- 43.8% chance to OHKO
252+ SpA Choice Specs Tangrowth Leaf Storm vs. 252 HP / 4 SpD Garchomp: 354-417 (84.2 - 99.2%) -- guaranteed 2HKO
252+ SpA Choice Specs Tangrowth Leaf Storm vs. 252 HP / 96+ SpD Clefable: 279-328 (70.8 - 83.2%) -- guaranteed 2HKO after Leftovers recovery