There's a couple of bugs with the Mirroring Raven (deal 4 random damage when a follower gains faith):
- It doesn't work with the unit that gains an extra faith whenever a follower gains faith.
- Copying a "gain faith at the start of combat" unit will still only proc this effect once.
- Adding a "gain 1 faith at the start of combat" buff onto the same unit will also not trigger it a second time.
- Nor will the "gain 2 faith on death" unit trigger Mirroring Raven twice if it's enchanted with "gain 1 faith when damaged" (unless of course it survives the hit)
- What will work however is the unit that gains faith on each attack. Make it attack 4 times and Mirroring Raven is gonna blast 4x as well.
I don't know if these interactions may be intended, but they should probably all work given they're nothing special. Except the "gain 1 more faith" unit (after all one might argue it just increases the faith gain) but I think that one especially should work since it's pretty bad.
Another notion on endless mode: I'm not sure how good it is to have random Doppelgangers, Barricades, Firework Masters, and Black Knights in there. They're hard counters to certain strategies (e.g. hyper-buffing a single unit) which leads to fewer strategies being viable there, exactly the reason why you hesitated implementing endless in the first place. I'd rather see enemy units with a lot of stats in the first place, and from there focus on softer effects like multiple attacks, revives, or not taking more than 25% of their HP in one hit.