Tangela
Type Tier
Grass UU
Statistics
Stat
HP
65
 333
Atk
55
 208
Def
115
 328
SpA
100
 298
SpD
40
 178
Spe
60
 218
Name Item

Double Powder Tangela

 Leftovers
Moveset
~ Stun Spore
~ Sleep Powder
~ Giga Drain
~ Reflect / Synthesis

Double Powder is a good thing to have, so status away. Giga Drain with the Special Attack makes Tangela a good Rhydon/Marowak counter. Reflect can help the team, or Synthesis keeps Tangela in the game longer.

Other Options

Swords Dance and Body Slam should only be used together. It can work in underused for something unexpected, but you probably would want to leave this job to Meganium or Venusaur. You could also use Growth to bolster the strength of Giga Drain, since it's tough working with 8 PP.

Opinion

Nintendo really must not have liked Tangela, because they took away an astonishing 120 points from its Special Defense, essentially taking away any of Tangela's tanking ability. Not learning Leech Seed is a bummer too. However, Tangela has potential in underused for absorbing hits from things that only have physical attacks.

Counters

Exeggutor because Tangela can't do anything to him. Skarmory, Zapdos, Moltres, Charizard, Jynx, Houndoom, Gengar, Articuno, Muk, Heracross, Tentacruel, Victreebel all work because they have a move that smokes Tangela (especially Zapdos through Articuno easily smack through down Tangela's abominable Special Defense).