Just to give you a heads up, Ob nixilus' effect does not work with
slaughter games Because you are searching their library and they're not searching it themselves. If you added hell-hole flailer to this deck and pump him up with spell enhancements (like
lightning talons,
sure strike or
kindled fury and then sac him then that's a huge health swing and your creatures all get played for cheap due to Rakdos on the field. I would recommend adding
morgue burst because it gives you creature recursion, deals damage, and if rakdos is on the field you can play that creature for less mana depending on how strong it is. Add some thrill kill assassins and
rakdos shred-freak then you'll have a quick and painful deck. If you add the Guildgate and some
bloodfell caves you can get that dual land action going and gain some health in the process.
Also some other good creatures to add would be
carnage gladiator, carnival hellstead,
cryptborn horror,
dark revenant (if you play the
eater of hope),
drainpipe vermin (for hand control),
grim roustabout (don't unleash him, use him as a wall that regenerates),
guttersnipe,
rakdos ragemutt, and
splatter thug would all be good for this deck.