Ustinak would be a little scarier if he walked slowly and you were in a small corridor and it took a while to get out. He runs so fast he is easy to dodge.
When he stops I run up and melee him and then run away, of course it does no damage but after months of play he is no longer dangerous at all on any difficulty.
I always use the inf ammo magnum and magnum master on him when I play as Sherry. He goes down very fast. But sometimes I tease him and run up and hit him with the stun stick to make him chase me. He's funny.
I join people's online campaigns almost every day, if they are playing as Jake and have inf ammo turned on. Maybe I will see you online sometimes.