The closest alternatives I can see (not equal, just closest to the power level of negator) that you could cast would be:
Spined Fluke
Color= Black Type= Creature - Horror Cost= 2B US(U)
Text (US): 5/1. ; When ~this~ comes into play, sacrifice a creature. ;

: Regenerate ~this~.
If there are no other creatures in play when this card comes into play, you must sacrifice this card. [Urza's FAQ 1998/10/05] See Rule 410.10a.
Note - Also see Comes Into Play Abilities, Rule 410.10a.
and
Juzam Djinn
Color= Black Type= Creature - Djinn Cost= 2BB AN(U2)
Text (AN+errata): 5/5. ; At the beginning of your upkeep, ~this~ deals 1 damage to you. [Oracle 1999/09/03]
Neither of them are great, but then, even with its drawback, Negator is Pretty damn good and there aren't really that many creatures that compare.