Starting in Generation IV, Entry Hazards are a new game mechanic that can disrupt the flow of battle. These are great moves for competitive play, since switching out Pokemon and taking no damage for it have frustrated players. These moves are Spikes, Toxic Spikes, and Stealth Rock. Each one is unique and has its own characteristic to add to the battle.
Let’s start with Spikes, a Normal-type move. It is the considered the most basic Entry Hazard, but using it even once can help topple a formidable opponent. Spikes, when used, are followed by the message, “Spikes were scattered around your team’s feet”. This means that switching out your Pokemon (this includes force-switching, like using Roar, Whirlwind, etc.) will cause the Pokemon that takes its place to take damage. When this happens, they will take damage equal to 1/8 of their maximum HP. Since Spikes is a ground-based move, it will not affect Flying-type Pokemon or those with the ability Levitate. They will still be out there for the next Pokemon, so the effort is never in vain.
Another pro to this move is that it can be used to a maximum of three times and still do damage. The first layer takes out 1/8 of the maximum HP, the second one takes 1/6, and the third (and any subsequent layers) will drain Ľ of the opponent’s HP. It is a time-consuming strategy, but it will be worth the effort. Toxic Spikes is built off of Spikes, but has a slightly different effect: it doesn’t take out HP. When Toxic Spikes are in effect, the Pokemon that comes out will be poisoned and take out 1/8 of its HP each turn. Like Spikes, you can add layers, but the maximum is at number two. However, instead of poisoning the opponent, it will badly poison them, taking out even more HP each turn.
In my opinion, this move isn’t as effective as Spikes, since it takes some time to work, but it is just as deadly. The final Entry Hazard is Stealth Rock, which deals damage according to the Rock-type matchup. This is labeled by the message, “Pointed stones float in the air around your team”. When a Pokemon switches out, the new one will take damage according to its matchup to Rock. If it normally deals regular damage, it will take out 1/8 HP, much like the first layer of Spikes. A supereffective hit will take out Ľ of the HP, and a double-effective (both types are weak to Rock) will eat up half of its HP. The same works for ineffective: 1/16 and 1/32 HP for “not very effective” hits. This means that you can take out Pokemon like Charizard (Fire/Flying-type) very easily.
The only con to all these moves is that they can be taken out by the move Rapid Spin. It is a very weak move, but it can remove all Entry Hazards at once. Pokemon that know these moves are usually called “Rapid Spinners” by competitive players because of their use, which is fitting. As you can see, Entry Hazards are worth the time and effort needed to master a strategy involving their use.