Key steps to the side so he can see the person attacking Leonidus. Once he has a clear view of the derro, he unleashes a stream of curses he heard from a muleskinner trying to urge his team through the heavy traffic at the gate at the misshapen dwarf.

Spoiler: Attack
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Vicious Mockery WIS save (DC 13) or take (1d4)[2] Psychic damage and Disadvantage on his next attack roll.