DLC Scarecrow Boss Issue? Stun?

[Colx]

I'm loving the game and hope to beat it with 5 boss cells. Saying that, the one boss I'm having trouble with is the Scarecrow.

I don't know if it was intentional or not but I've seen other bosses get stunned (either through the hook hand, stun grenade, or any shield after a parry). Can the Scarecrow boss be stunned at all? The latest run I had was stunned based (a shield that provided longer stun time, the hook arm and pulls them in and stunned, and the stun grenade) and none of these work against them.

Was this intentional as a challenging boss or a bug?