Entry Hazards are moves that add an effect to the battlefield that do damage, poison, or otherwise inflict an effect on your opponent every time a Pokemon of theirs switches in. Some of these effects will do damage to a Pokemon that has already been hurt by them, others will not. These may not do a whole lot on their own but these entry hazards can dynamically shift the battle and completely influence defensive and offensive strategies.
In a general sense offensive strategy players have a hard time switching on a hazard field because they tend to be more frail and can't survive the extra damage they're taking. On the other hand defensive strategy players have to be careful not to switch in a Pokemon that can wall to remove the hazards and end up losing them.
There are different kinds of entry hazards:
- Spikes can be layered and at the highest layer you can have 3 Spikes active. Each layer doing more damage. Spikes do not have an additional effect.
- Layer 1 Spikes does 1/16th damage
- Layer 2 Spikes does 1/8th damage
- Layer 3 Spikes does 1/4th damage
- Spikes do not work on Flying type Pokemon
- Spikes do not work on Pokemon with the Levitate Ability
- Spikes do not work on Pokemon with the Magic Bounce Ability
- Spikes can be removed with the move Defog
- Spikes can be removed with the move Rapid Spin
- Toxic Spikes
- Toxic Spikes can be layered and at the highest layer you can have 2 Toxic Spikes active. Each layer inflicts a different level of Status to your opponent.
- Layer 1 Toxic Spikes inflicts PSN status to your opponent.
- Layer 2 Toxic Spikes inflicts TOX (BADLY PSN) status to your opponent.
- Toxic Spikes do not work on Flying type Pokemon
- Toxic Spikes do not work on Steel type Pokemon
- Toxic Spikes do not work on Poison type Pokemon
- Toxic Spikes do not work on Pokemon with the Levitate Ability
- Toxic Spikes do not work on Pokemon with the Magic Bounce Ability
- Toxic Spikes can be removed with the move Defog
- Toxic Spikes can be removed with the move Rapid Spin
- Stealth Rock
- Stealth Rock can only be placed in a single layer. Unlike Spikes the amount of damage it does is based on the Pokemon's individual effectiveness against Rock type moves.
- Stealth Rock do not work on Pokemon with the Magic Bounce Ability
- Stealth Rock can be removed with the move Defog
- Stealth Rock can be removed with the move Rapid Spin
- Sticky Web
- Sticky Web is a unique move as it lowers the enemy Pokemon speed on switch in by 1 level. This can be crippling for a team reliant on outspeeding their opponent.
- Sticky Web can be removed with the move Defog
In a general sense you're going to see Stealth Rock, Spikes, Sticky Web, and Toxic Spikes (In that order of frequency) based on the strategy of your opponent. Stealth Rock can do big damage to threats like Charizard Y and pre-Charizard X, not to mention hitting Flying type for 1/4, it is a huge threat in the meta game and can make what would be a quick switch and sweep into something a little more careful and cautious. Spikes are in general a good idea for the potential 1/4 damage it can afflict and is good for sweeping teams or teams that force switches like Whirlwind or Roar teams. Sticky Web is interesting but the most viable Sticky Web user is Galvantula and... well it doesn't really do much else than set up this move. It does allow sweeping teams to easily outspeed the competition and can cripple revenge killers. Finally Toxic Spikes is good for defensive teams but is less threatening since it doesn't have an immediate damage factor that the Stealth Rock and Spikes offers nor the on field disadvantage that Stick Web offers. All in all these entry hazards are easily game changing and shouldn't be considered lightly when forming your teams.