My intention is for her first niche to be as a reliable finisher on enemies that other units have whittled down. As long as an enemy has 5 HP or less, Yowl can always kill it, whereas other units do 3-4 damage and may miss, so she has a slight advantage in being the one for a final hit.
Besides that, I intend for her secondary niche to be as a good unit to position for allies to proc follow-up attacks on, since she has above-average damage, and her passive lets her avoid being targeted if other units are in range (so if she goes into a vulnerable spot or behind enemy lines to position for follow-ups, she's not in as much risk of getting surrounded and destroyed by enemy units doing their own follow-up attacks on *her*).
It seems so far like she's one of the less favored units among players. I'll be giving her a slight buff next update (+1 movement, and allowing her to traverse past enemy units, to be able to more freely position herself which I hope will help with that secondary follow-up attack niche).

