This page shows the strategies to successfully beat Victreebel considering Victreebel's possible movesets. For details of Victreebel, such as evolution chart, CP and HP, refer the link above.
Super effective moves
Victreebel is weak to the types below. For list of moves by types, tap the name of types.
Best Pokemon 1
Victreebel's moveset
The combination of Razor Leaf and Solar Beam is considered as the best moveset for Vicreebel as an attacker and a defender.
When Victreebel use only grass-type moves, Charizard is one of the best options. It uses fire- or flying type fast/charge moves which are very effective against Victreeble while cut damage of grass-type moves. It has high stats along fire-type Pokemon and its fire-type moves can get same type attack bonus (STAB).
Optimal moveset for Charizard to beet Victreebel is Wing Attack (or Ember) and Fire Blast. Usually Wing Attack and Fire Blast is considered as the best moveset for Charizard as an attacker. On the other hand, Ember is super effective against the grass-type Pokemon.
Other options
Other fire-type Pokemon works as well.
Pidgeot is easy to get. It uses flying-type moves with STAB are super effective against Victreebel and can reduce damage of grass-type moves.
Dragonite has high stats along all Pokemon, and grass-type moves are not effective against it.
For list of fire- and dragon-type Pokemon, tap the name of type below.
When Victreebel use only poison-type moves, Arcanine will be one of the best Pokemon to fight against it due to its attack performance. Arcanine has higher attack stats thant that of Carizard and can use Fire Fang which is more powerful than Ember. Arcanine cannot reduce damage of poison-type moves but use fire-type moves with STAB. Beating Victreebel faster means receiving less damage as a result.
Optimal moveset for Arcanine to beat Victreebel is the combination of Fire Fang and Fire Blast. Those moves can damage Victreebel effectively due to type match-up and w/STAB.
Other options
Other fire-type Pokemon will also work.
Alakazam can use Psycho Cut, the most powerful psychic-type fast move.
Slowbro has well-balanced stats and can use psychic-type fast/charge moves.
Golem's moves are not super effective against Alakazam but can reduce damage of poison-type moves.
Arcanine will be the best one even when Victreebel's movest is the combination of grass- and poison-type moves. Arcanine use fire-type moves are super effective against Victreebel with STAB while cut damage of grass-type moves. For the best moveset, refer notes above.