Is Archbishop Benedictus a decent replacement for Elise in an Highlander deck?
As has been pointed out Benedictus doesn't make sense in Highlander as it directly counters what you're trying to do with the deck (get to your "no dublicate" synergy cards like Kazakus, Raza as well as your finisher cards like Anduin, Velen, Lyra as fast as possible).
I'm not totally sold on Elise in Highlander Priest either. I mean in a way she does the same thing as Benedictus but obviously in a way less drastical way. She adds a card to your deck which essentially delays you reaching your finisher combos. On the other hand the five cards created oftentimes can win you the game as well, if they're low mana cost which enables your Anduin/Raza hero power spamming. But I don't think she's a must-include in the deck, actually I don't play her.
I've been having fun with the Penguin OTK variation of Highlander Priest lately. So the game plan is to pull your Raza and Anduin asap to get your hero power down to zero mana and do damage. Your OTK combo consists of:
1 Hero Power for 2
2 Play Velen
3 Hero Power for 4 (Velen)
4 Play Mirage Caller and copy Velen
5 Hero Power for 8 (double Velen)
6 Play Penguin or 0 mana spell
7 Hero Power for 8 (22 damage dealt already)
8 Play 0 mana spell (Silence / CoH)
9 Hero Power for 8 (30 damage)
10 Play 0 mana spell
11 (Hero Power for 8 (38 damage)
...
Normally 22 is enough so it's a 3 card combo (Velen, Mirage, 0 mana spell or Penguin). Of course you need to first pull and play Raza and Anduin.
Before you just destroy their board with Doomsayer, Shadow Words, Thalnos + Spirit Lash / Holy Nova / Dragonfire Potion, other spells off Lyra or Auchenai+CoH. Ideally you get another Dragonfire Potion off Shadow Visions.
Not too easy to pull of but quite fun when it works.
In generall I've been having fun with these OTK decks lately (Exodia Mage / Beardo Paladin / Penguin Priest).