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The holder can switch out, even if under the effects of Ingrain, Arena Trap, Magnet Pull, Shadow Tag, Block, Mean Look, Spider Web, Bind, Clamp, Fire Spin, Magma Storm, Sand Tomb, Whirlpool, or Wrap. Pokemon that have used Ingrain and or have the ability Suction Cups are still not affected by Roar and Whirlwind. A Pokemon locked into Ice Ball, Outrage, Petal Dance, Rollout, Thrash, or Uproar will still not be able to switch out.
Shed Shell's ability to allow the holder to escape the grips of trap-related abilities and moves is extremely beneficial for a lot of Pokemon.
Shed Shell sees the most use in the OU metagame, commonly held by Skarmory and Forretress. The reason for this is Magnezone, who is capable of trapping both of them with its ability, Magnet Pull, and defeating them with Thunderbolt or Hidden Power Fire, respectively. Magnezone completely stops Skarmory and Forretress from setting up multiple layers of Spikes (or other entry hazards) if they do not use Shed Shell.
In the UU metagame, Shed Shell doesn't see a lot of use, but it is still helpful with Dugtrio and Magneton are running around. Chansey is one of the most common holders of Shed Shell, because it allows her to switch out of Dugtrio, who loves to trap Chansey and defeat with repeated Earthquake attacks. Registeel is also a common user of Shed Shell, allowing it to switch out of Magneton, who can set up Magnet Rise and Substitute, as well as Dugtrio, who destroys Registeel with Earthquake.