Considering you're serious about BH protection, I'm assuming you're using this for Gold? It would explain using Oty over Charger too. If so, I would heartily recommend Spectre over Frog since it quickly gets both faster and more durable. FFQ over Wyrm is usually more optimal, but in this deck you may want to keep the speed. The only thing I'm really missing besides a Spectre is a Steamie. I cannot begin to count the amount of games that Steamie has won me in all the leagues. It's insane.
Even with the single-target CC protection from Cloak, I imagine you run into mass CC sometimes and PC a -lot-. As it turns out, Steamie isn't that slow either, -especially- if the opponent has 200 HP. It also works perfectly with FFQ, should you choose to consider her. Steamie does contend for Water if you pack a Spectre and an Uli, but most games you only want to play one of them. Some games you want to play Uli and Steamie, some you just rush with Spectre and Steamie later on.