When a Pokémon with Tablets of Ruin is sent into battle, Tablets of Ruin decreases the Attack stat of all Pokémon on the field other than Pokémon with this Ability by 25%. The effect does not stack if more than one Pokémon with Tablets of Ruin is on the field. The effect ends when no Pokémon with Tablets of Ruin are in battle.
This does not affect self-inflicted confusion damage for Pokémon other than the one with this Ability. The damage dealt by Foul Play is affected by this Ability, unless the move user is the only Pokémon with Tablets of Ruin as its Ability on the field. For example, if a Murkrow uses Foul Play against an opponent when Wo-Chien is on the field, it will deal reduced damage. If Wo-Chien uses Foul Play against an opponent, its damage won't be reduced.
Strength Sap is unaffected by Tablets of Ruin; the HP recovered will be the same regardless.