Since death already have Bone Wall, and this card functions like Armagio, not only absorb but also reflection, means the death of either mirror or attacking creature will generate 2 charges for Bone Wall. So if mirror reflects every hit, it can't be too tough or the Bone Wall will become almost unbreakable (Mirror also block attacks to Bone Wall while in play). I would prefer "inflict damage to attacking creature if received damage is higher then X" to specialize it's use. With Gravity Pull, you would also have to choose when to active this effect (to kill something like dragon, highly grown Forest Spirit etc). Active this card too early would be a waste. Even with 1HP left, it still inflict full damage back to attacker.
Changed version:
Pain Mirror
Cost: 3
0/8
"Inflict damage to attacking creature if received damage is higher then X"
: Gravity Pull
Pain Reflector
Cost: 3
0/10
"Inflict damage to attacking creature if received damage is higher then X"
: Gravity Pull
X = around 5 IMO
Optional:
"Mirror doesn't take damage if the reflection works" (Maybe OP?)
How does this sound?