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Deals damage and traps the target for 4-5 turns, dealing 1/16 of the target's maximum HP at the end of each of those turns and preventing the target from switching. If the user is holding a Grip Claw, it traps the target for 5 turns all the time. If a trapped Pokemon uses Rapid Spin, it will be freed. If the user is holding a Binding Band, the damage dealt at the end of each turn increases to 1/8 of the target's maximum HP. The target can still switch out if it is holding Shed Shell or uses Baton Pass, U-turn, or Volt Switch. This effect is not stackable or reset by using this or another partial-trapping move.
Sand Tomb, like all the other trapping moves, is incredibly gimmicky. Sand Tomb can, on occasion, allow a Pokemon to easily set up, but it also requires that it traps the right Pokemon, which takes a lot of luck, skill, and prediction to actually accomplish. It might allow a Pokemon such as Garchomp to capture a Pokemon that does not pose any sort of threat to it, like Forretress, and set up Substitutes and Swords Dances (provided the Forretress is running Volt Switch or Toxic over Gyro Ball), but that really is the extent of what Sand Tomb can do.
Whirlpool is a Water-type equivalent.
Clamp is a physical equivalent.
Fire Spin is a Fire-type equivalent.
Magma Storm is a Fire-type equivalent, but with greater Base Power.
Bind is a physical Normal-type equivalent with lower Base Power.
Wrap is a physical Normal-type equivalent with lower Base Power but higher accuracy.