Strictly speaking she isnt completely awful, but you should be glad Scarecrow is the free SF Ringleader.

Her skills are oriented towards damage, damage, and more damage, and dealing it in different ways. Unfortunately she gets the short end of the stick by being a melee unit with a -range skill, meaning it is entirely possible for some enemies to walk past her and she can't do anything about it (hope you have a good backline I guess).

Her real problem is Alchemist exists, and when she comes out, basically does her job but better, mostly by tanking almost anything (she can solo Yegor without player input just by outlasting him, which Executioner cant do). Also Hunter comes right after her, and hunter is legitimately a very good unit, which discourages rolling for her on her last weeks.

There's a joke her role is to run in and die, and.... yeah it's not entirely innaccurate. She will deal damage before she explodes though. Probably. As long as enemies dont walk around her instead.

Kind of a meme. A melee unit who, unlike executioner, is actually good at it. Basically, she has infinite shield that keeps stacking as long as she attacks. Most bosses are not meant to fight this sort of thing, so she basically can destroy Yegor with no player input outside of telling her to go attack him. She isn't invincible or invulnerable, and is particularly vulnerable to burst damage enemies (Hydras come to mind, or SWAP Jaegers), but basic enemy fire wont even phase her.

Another issue is that friendly SF aren't invulnerable to stun, and some enemies can stun her. When that happens, she goes down pretty hard because she can't replenish her defenses. Otherwise, her overwhelming defensive ability lets you faceroll most encounters.