Hi, one of my players has used command undead on a skeleton with fast healing. It was dropped (to less than 0) by another monster. My question is, when it regenerates back to life, will it still be under his control? Looking for any rules sources that clarify this, if they exist. Thanks.
Fast healing is not regeneration. If an undead is dropped to 0 or less HP then it is destroyed, ending fast healing. It does not come back.
If you're talking about a bloody skeleton, then that does not come back to life due to the fast healing ability but rather their deathless ability. Their fast healing only resumes when they come back due to deathless.
I'm not aware of any specific rules that cover this, but it's still the same skeleton, so I'd say your player would still have control.
Thanks, and yes it is a bloody skeleton.