Its been a little bit quiet now and maybe necro, but im going to say it here: all imp characters shouldn't have type 2,3,4 and 5 immortality and the regen stuff shouldn't be included since imps shouldn't scale to sinners/royal demons.
In regards to the immortality stuff, its been shown, multiple times in fact, that imp type demons can die. Millie has been stated to have killed multiple imps in "
The Harvest Moon Festival" (S1E5), while another imp(?) (probably not an imp but still a low class demon) named Chaz was shown and confirmed to be killed by the end of "Exes and Oohs" (S2E3), while Moxxie's mom was also implied to have been killed as well. So obviously immortality types 2,4 and 5 dont apply here. The only type of immortality that could be applicable to imps would be the type 1 immortality, but even that claim is based off the idea we're still scaling imp immortality to sinners, which given the facts, we really shouldn't be doing that in the first place. For all we know, imps are just as mortal as any actual human, the only difference being they are a bit stronger than one.
As for regen, the answer is simple: no imp demon has been shown to have the same level of regen as that of a sinner. The only notable feat of regen would be Blitzo recovering from a gunshot wound in "Murder Family" (S1E1), but we have no timeframe for the healing and even highballing it would put Blitzo at an inferior regen level compared to that of a sinner.
So yeah, imps should have their immortality removed and their regen downgraded. There are too many anti-feats and statements to suggest imp demons are comparable to sinners or royal demons and until a feat or statement states otherwise, they should be taken off the profile for the time being.