Nurglings.
Also, here are some tidbits from some guys that have a preview copy:
Gabriel Seth - bunch of buffs including Chapter Master, extra AP, extra hit on 6 in the Fight Phase
No more sang Priests with jump pack/bike in codex. Still in index. Ditto for tons of other index-only options.
lib dread 20pts cheaper
termie lib down 25pts
Chaplain termie down 15pts
Astorath's weapon +1s
Tycho the Lost new "dead mans hand" (Melee S:user AP-2 Dd3)
Cpt Tycho also gains dead man's hand
termie captain down 15pts
16 new units (lieutenants, primaris stuff, planes, anti air vehicles, etc)
techmarine down 13pts
Tactical squad - sergeant may now take a Melta Bomb
Sanguinary Guard down 2 points
Chapter Banner nerfed - was immune to morale, now +1LD. Bonus to wound rolls stays the same.
Sanguinary Novitiate new unit (identical to basic apothecary with Bloody Blood blood name)
DC Dread down 38pts
Terminator Ancient new unit
Company Champion down 16pts
Terminator assault squad down 5ppm
Furioso Dread down 52 points
Blood Talons now S+4 -2AP 3Damage, reroll failed hit and wound rolls for this weapon
Assault marines now get melta and plasma guns