I give his own skill page. Mine is max enhanced (both unit and skill page) already (400 pulls for both Mereo and Black Asta, and playing since launch, I should get that already). The skill page has 50% chance of giving 10% mobility buff when max enhanced while his skill 2 has 0% chance to grant an ally 15% Increased Mobility. So if my stamina is at 75% for the target, the target will get 2 conseuctive turns. It is completely RNG. This is just one lucky run and happens that I get to record it :) Make sure you give him the advanced speed set and speed craved stone (max support talent)