Like if I use Shell Smash, will all 3 of the stat drops be regained?
If any of the holder's stats are decreased any number of stages, White Herb will immediately negate that stat decrease. This effect will occur regardless of which player's Pokemon caused the decrease. This item is consumed after use. The White Herb can come in handy for Shell Smash sweepers, since it negates the Defensive stat drops that comes with the move, effectively giving the sweeper +2 Attack, +2 Special Attack, and +2 Speed with no drawbacks. Smogon