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Prevents the target from switching out. The target can still switch out if it is holding Shed Shell or uses Baton Pass, U-turn, or Volt Switch. If the target leaves the field using Baton Pass, the replacement will remain trapped. The effect ends if the user leaves the field or if the user or target faints. Note that if the user then uses Baton Pass, the effect will now end. Pokemon protected by Magic Coat or the ability Magic Bounce are unaffected and instead redirect this move back to the user. Does not prevent the effect of Eject Button. If the target is hit with Roar or Whirlwind while Block is in effect, they will be forced out as per normal.
Block is not a frequently seen move competitively. It can, however, be effective in some cases, especially if combined with sleep moves. For example, Gastrodon can use Block + Yawn + Memento to give a completely free turn to a dangerous set-up sweeper. This move could also see some use, for example, in Toxic stalling. Unfortunately, though this move can potentially offer free setup, this move can no longer be effectively used alongside Baton Pass.
Mean Look is a Normal-type equivalent with different distribution.
Spider Web is a Bug-type equivalent.