Gus Allen (Zombie)
Obtained from Rebirth of the Dead Special Event.
Has a split evolution at SSS. Can be evolved to Gus Allen (Human) if you happen to have an SS Vaccine to use as Evolution Material.
Otherwise, you can use a DRA Ring to further evolve his Zombie form to DRA.
The 20% Skill Boost is applicable to any card, which is pretty nice, especially for Support cards.
However, the major downside of this is the 20% increased chance of receiving Status Effects.
This highly limits its use, especially in dungeons with particularly nasty Status Effects flying around like Paralysis or Blindness.