Cacturne
This pokemons is probably a more supportive pokemon than something more aggresive like it should be e.e, in anime and even at bulbapedia it can learn a lot of fighting and poison moves, this pokemon supussed to be more for pvp than for hunt. Anyway after alot of tests, i think it needs something else to improve its way to battle in pvp because the moves it has are too weak sometimes. The best moves fling and needle arm sometimes doesnt hit, and the other moves are all basics, its just a pokemon with 4 good moves, 6 TRASH moves, who did it, just add the other 6 moves to complete its moveset, not thinking exactly in how good or bad it would be ...
Moves:
Sucker Punch - m1 - level 60 - 10s <-- too weak
Poison Sting - m2 - level 60 - 10s <-- too weak <- this move its a lvl 10-30 pokemon move.
Energy Ball - m3 - level 60 - 10s <-- maybe okay but weak.
Grass Knot - m4 - level 60 - 20s <-- good but 20s is too much. 15s would be better.
Stun Spore - m5 - level 60 - 30s
Ingrain - m6 - level 70 - 45s <--good
Solar Beam - m7 - level 62 - 25s <- not so good.
Spiky Shield - m8 - level 65 - 50s <-- good
Fling - m9 - level 65 - 40s <- good
Needle Arm - m10 - level 70 - 45s <- good
My suggestion is next:
Moves:
Poison Jab - m1 - level 60 - 15s
Sting Gun - m2 - level 60 - 15s
Faint Attack - m3 - level 60 - 15s
Grass Knot - m4 - level 60 - 15s
Stun Spore - m5 - level 60 - 30s
Ingrain - m6 - level 70 - 45s
Solar Beam - m7 - level 62 - 25s
Spiky Shield - m8 - level 65 - 50s
Fling - m9 - level 65 - 40s
Needle Arm - m10 - level 70 - 45s
Passive: Bullet Seed
Having these moves with a strong damage, this pokemon would become alot better, also all the moves suggested are main moves from this pokemon, it may not be poison but he can learn a lot of this types because its a captus, with a lot of spikes and his fighting style makes them perfect.
Look that im not suggesting something Op , something that could change him all, these 4 changes would be enough.