On the first turn, the user will dive down for one turn and become invulnerable to most attacks, with the exception of Surf and Whirlpool, which will do twice the damage to the submerged Pokémon. The user can also be hit underwater if it was previously targeted by Lock-On or Mind Reader. Sandstorm, Hail, and Shadow Sky will not cause damage during the semi-invulnerable turn.
Pokémon can be caught during the semi-invulnerable stage of Dive.
Dive's base power is 60.
Dive can be used as part of a Pokémon Contest combination, with the user gaining extra two appeal points if either the move Rain Dance or Surf was used in the prior turn. It can also be used to start a combination, causing Surf to give extra three appeal points if used in the next turn.
Pokémon can no longer be caught during the semi-invulnerable stage of Dive.
The user may now be hit while underwater if it is attacked by a Pokémon with No Guard, or if the user has No Guard themselves.
If a Power Herb is held by the user, Dive can be executed in one turn.
Outside of battle
Dive allows players to go underwater in dark patches of water while they are surfing. The only regions in which these spots (and the HM itself) have been seen are Hoenn and Unova. Thus, it is only an HM in Generations III, V, and VI.
You'll dive underwater, get the Dive status condition, and do damage to an enemy on the next turn. You'll evade items or moves while you're underwater. But Surf and Whirlpool will hit you, so be careful!
In the manga
In the Pokémon Adventures manga
The user dives underwater while letting passengers hold onto it.
Unlike Whirlpool and Defog, which can be freely known by a Pokémon sent forward to Generation V when said Pokémon is transferred from a game they are not an HM in, a Pokémon with Dive will be prevented from being migrated to Generation IV even in Pokémon FireRed and LeafGreen, where Dive is not usable, required, or available to the player without trading.
Dive is the only HM move not to have been featured in the anime so far.