Ability₂₁₇-Shadow Tag

Shadow Tag prevents all adjacent opponents from fleeing (including Teleport) or switching out while the Pokémon with this Ability is on the field.
⚠️However, if a Pokémon with Shadow Tag switches in,
opponents are not prevented from switching out for that turn.
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⚠️Using Baton Pass, U-turn, Volt Switch, Flip Turn, or Parting Shot will still cause the Pokémon to switch out.
⚠️Having the Ability Run Away or holding a Smoke Ball allows the Pokémon to flee or Teleport, but not switch.
⚠️If the player does not switch out a fainted Pokémon and instead attempts to flee, they will not be affected by a wild Pokémon with Shadow Tag.
⚠️Shadow Tag does not affect allies.
🔵Gen⁴⁺
Shadow Tag now makes the Pokémon immune to the effects of other Pokémon's Shadow Tag. Holding a Shed Shell allows the Pokémon to switch out, but not flee or Teleport.
🔴Gen⁶⁺
Ghost Pokémon are now immune to Shadow Tag.
In Pokémon X/Y, Shadow Tag will not prevent roaming Pokémon from fleeing
because they will flee before the battle before even starts.
~Bulbapedia