3. What you'd expect - decreased Bth (as long as the monster gets its Bth from DEX).
EDIT: I think it's important to say that monsters might get bonuses (damage/Bth) from different stats than usual. Afterlifex, for example, gets his damage and Bth from CHA, which is why he does so much damage and has so high accuracy with 0 STR/DEX/INT.