There is only one Big Root in the game, and it can be found on Route 214 just south of Veilstone City. It will be visible in the overworld as a Pokéball item, among a maze-like arrangement of picket fences.
The Big Root is a Held Item. When a Pokémon holding the Big Root uses an HP-stealing move, the move will replenish 30% more health. It does not cause more damage to the target Pokémon.
Big Root Location (Step-by-Step)
The only Big Root in the game is found on Route 214, about halfway between Veilstone City and the Hotel Grand Lake.
From Veilstone City’s Pokémon Center, head east on the main street, then turn south.
Continue south and leave Veilstone City using the southeastern entrance gate.
Once you’re on the other side, head southeast going past the berry plot and toward the three parallel lines of picket fences.
Enter either of the two alleyways created by the fences (doesn’t matter which one you go through here).
Just keep following the gaps in the fences as you head south.
When the fence placements start to become more elaborate, stick to the eastern path (pictured below).
Eventually you’ll see a signpost to the west. Move toward the sign, and head directly north of it.
The path will lead to a dead-end, and a Pokéball item will be visible in the overworld in the left-hand corner. This is the Big Root.
What Does the Big Root Do?
The Big Root is a Held Item. When a Pokémon holding it uses an HP-stealing move, the Big Root allows the move to replenish 30% more HP than it normally would.
This works conversely if the holder of a Big Root uses a draining move on an opponent that has the Liquid Ooze ability; the damage inflicted on the user of the draining move will be 30% greater.
The following moves are empowered when the user is holding a Big Root:
- Aqua Ring
- Drain Punch
- Dream Eater
- Giga Drain
- Leech Life
- Leech Seed
- Mega Drain