@kqaosphreak Excellent! Thank you for the feedback. Sorry it took so long to respond, I was away from home.
So first the CON thing. No, the CON mod is only added to the Hit Point Pool. No double dipping modifiers 😄👍. (Edit: As long as the Modifier is only applied once, I don't see why you couldn't add it to the Shield pool. Adding the modifier to the Hit Point Pool was just made more thematic sense to me.)
Now the second thing. So this seems a bit more abstract, and I've been thinking about it since Saturday. Honestly, on paper it doesn't seem that bad. But it depends on a lot of factors. What level is the Rogue, how many hit dice did they allocate to the Shield Pool, that kind of thing. So... we need a Rogue as an example.
Johnny McBackstab, 2nd Level, Custom Lineage Rogue.
Johnny has a Dexterity of 18 and a Constitution of 12. At level two he would have:
10 in the Hit Point Pool (8 starting and +2 from CON Mod)
and 5 (average rounded up of 1D8) in the Shield Pool.
Johnny has a Proficiency Modifier of +2, so he normally heals 2 temp HP to his Shield per round till it is maxed out at 5. But while hiding or in half cover this improves to 4 per round, so it regens quicker, but the maximum doesn't change. When out of combat Johnny is fully healed in one round. So lets check in at level 5.
Johnny McBackstab, 5th Level, Custom Lineage Assassin Rogue.
Johnny has a Dexterity of 20 now and still a Constitution of 12. At level five he would have:
13 in the Hit Point Pool (8 starting and +5 from CON Mod)
and 20 (average rounded up of D8 four times) in the Shield Pool. This is assuming Johnny put as many Hit Dice in the pool as possible.
Johnny has a Proficiency Modifier of +3, so he now heals 3 temp HP to his Shield per round till it is maxed out at 20. This would take 7 rounds if depleted. But what if he hides? Double the rate (6/round) would still takes 4 rounds to top off. Now this can be powerful as long as you don't get keep getting hit.
After thinking about it, I think the hiding its fine. But being able to dash to Full Cover and recover 15/round might be a bit strong. So I am taking it under advisement. It's good feedback.
As for the last point, proficiency plus hit dice is the same as doubling proficiency most of the time. In the example above with the 5th level Johnny, he would gain 7 per round. This might be a bit stronger then intended. (Edit: Part of the intent with the shield is for Players to utilized cover instead of just standing out in the open, and I figured the Regen bonus would be a way to incentivize that.)
There are a few unknown things about the setting that might skew it towards being less OP, like Lightning Infused weapons and ammo for breaking shields, using modern firearms, or not having magical healing in the setting. Its all a work in progress. I need to throw some dice at the problem and see where it falls on the Over/Under-Powered Scale.
Again thanks for the feedback, let me know if this cleared things up a bit.
RE: Its a Regenerating Energy Shield for D&D