Regen is too strong. Possible changes to Regen.
- Put a hard cap on how many times a follower can regenerate. The card would say stuff like "Regen 2" or "Regen 1". Basically a counter for how many times something can regenerate. The number would just count down as they are used, so you can easily see what you have left. This wouldn't really need a momentum cost anymore, though it could stay too. Having a counter is not too convoluted, and can be easily explained.
- Have regenerate not save you from death. Make it so regenerate just "regenerates health" over time. For example like this: for every card you play, any followers with regenerate, gain 1 HP. Or they just regenerate health per turn.
- Make it so it costs more, each time you regenerate. This is not really my favorite solution, but it would solve the problem and still make sense.
I like the first one the most.
And then add cards like "Turn undead" - "follower gains Regen 2"