Does overaccretion count as death? If so, then this basically disables SoFo for every single non gravity mark deck unless they can deal with the singularity immediately.
Overaccretion counts as death, but any deck can still use it, they will just activate it only twice and won't get BH either.
Now there's an idea I can get behind. For added simplicity (thinking of the text) Upon death, creates Singularity (BH if mark of

)
Benefits:
1. only two permanents can be destroyed for non-gravity-mark decks
2. cost is essentially 3

for each permanent destroyed by a non-gravity-mark deck (makes it more expensive then explosion, which it should be)
3. Anyone playing it at 0/1 runs the risk of having it zapped and having a singularity in their field
Does point three underpower it, though? Maybe, upon death, creates an anti-supernova. (?) a