Okay stats checks done. Major find is this, the new DLC characters carry over their stats when growing meaning you need to grow them ASAP if you intend to.
Edit: All DLC keep their stats when growing.
DLC Underground Female: 14 HP(+2), 1 ATK(+2), 0.7 SPD, 6 BP, 3 cost
DLC Underground Male: 13 HP(+1), 4 ATK(+0.4), 0.8 SPD, 6 BP, 3 cost
Underground Young Man: 13 HP(+2), 4 ATK(+0.5), 0.8 SPD, 10 BP, 4 cost
DLC Large Female: 30 HP(+5), 12 ATK(+3), 1 SPD, 10 BP, 3 cost
DLC Large Male: 25 HP(+4), 14 ATK(+4), 1 SPD, 10 BP, 3 cost
Large Young Man: 25 HP(+20), 14 ATK(+7), 1 SPD, 18 BP, 4 cost
Second thing I found, Sadako gives birth to other Sadakos. A Sadako mothered DLC female will get Sadako's +1 speed upon growth giving her at 1.7 a base. Apparently this doesn't effect the Underground Young Man.