You should almost make it vulnerable to things like
Cure wounds (as undead, since cause wounds heals it as undead)
Remove Disease (suppress disease for 1d4+1 rounds)
Purify Food and Drink (suppress automatic disease infection while engulfed for 1d4 rounds)
That kind of thing.
Edit - Hmm, I'd forgotten the cure wounds stuff was in Tomb Tainted Soul - still, if you're explicitly mentioning the inflict thing it's either a redundancy which should also include the positive energy effects, or should be removed as a redundant entry. So there.
Further edit - should it have some kind of "slurp up the goo" ability for people who've died from bloodburn (obviously automatic for those who die in its embrace)? Maybe a temporary power-up or an extra HD or something?