Question

Which is a better move for Serperior, Leaf Tornado or Grass Pledge?

Comments

Neither are particularly good, though I assume this is only for an in-game playthrough?

---

Do you mean Double battles or what?

---

Yes, it's for in-game playthrough.

---

Mostly normal battles.

Answer 1

Leaf Tornado has a 50% chance to lower opponent's accuracy by one stage and its accuracy is 90%. Its base power is 65. Grass Pledge accuracy is 100% and base power is 80. If you are using Serperior in Double Battles with Grass Pledge and ally Pokemon with Water Pledge or Fire Pledge, then it has some special effects.
When Grass Pledge is used in the same turn with ally's Water Pledge on the same turn, the ally moving second will use Grass Pledge with a power of 150, and create a swamp on the target's side of the field for four turns. This swamp quarters the Speed of all Pokémon on that side of the field.
When Grass Pledge is used in the same turn with ally's Fire Pledge on the same turn, the ally moving second will use Fire Pledge with a power of 150, and create a sea of fire on the target's side of the field for four turns. The sea of fire damages all non-Fire-type Pokémon on that side of the field for 1/8 of their maximum HP at the end of each turn.
So, for double battles with Fire Pledge or Water Pledge, your Serperior should use Grass Pledge or for other battles you should use Leaf Tornado.
Source 1: https://bulbapedia.bulbagarden.net/wiki/Grass_Pledge_(move)
Source 2: https://bulbapedia.bulbagarden.net/wiki/Leaf_Tornado_(move)

Comments

Only starter pokemon can learn Grass Pledge/ Fire Pledge/ Water Pledge, right?

---

Why is leaf tornado better than grass pledge in single battles?

Answer 2

You never told me what game you're playing, so I answered for every game where Serperior is obtainable during the main story.

BW and BW2: Grass pledge's base power is 50 in this game, so leaf tornado is stronger. If you have access to the other pledge moves, that means someone traded the other starters to you, and you should ask that person to take the starters back and give you a Kyogre instead. If you don't, then you should consider using Lilligant instead of Serperior because Lilligant has higher special attack and can learn sleep powder and quiver dance.
source
source
source
SM: Grass pledge's base power is 80, so it's better than leaf tornado regardless of whether you have other pledge moves.