Its a custom shadow that uses image/animation and follows player in X axis and stays on floor in Y axis.
All you need is a shadow sprite and animation 9900 that uses it.
(http://i.imgur.com/CiAaVLm.png)
State that controls the shadow:
;---------------------------------------------------------------------------
;H - Shadow
;
[Statedef 9900]
type = S
movetype= I
physics = N
anim = 9900
sprpriority = -9900
[State 0, PosSet]
type = PosSet
trigger1 = 1
x = 0+ceil(parent, pos X);sets shadow position to character's position X, you can adjust it with the number value on the left
y = 0
Create Helper sctrl under Statedef -3
[Statedef -3]
[State -3, Helper]
type = Helper
trigger1 = 1 && !numhelper(9900);spawns shadow if there is no shadow
helpertype = normal ;player
name = "shadow"
ID = 9900
stateno = 9900
pos = 0
postype = p1
facing = 1
keyctrl = 0
ownpal = 0
supermovetime = -1
pausemovetime = -1