Since Smokebomb requires both the Activation cost(AC) and the Casting cost(CC) to be paid to renew the temporary cloak, it seems like AC+CC should be a low value.
Smokebomb +
Stealth 2 acts almost like Immaterial (the weakness to AoE is still important)
HP of 1 is convenient as a weakness and to make the Stealth'd creature (named Ninja) only visible after Pandemonium because it would die to other AoE
I would suggest -1Atk, -1 CC.
Stealth 2
Smokebomb
AC+CC=low
AC=
|1
CC=2
|1
Atk=3|3-4
HP=1
=/=
(nightfall would allow creature to be seen without Pandemonium)
=
or
based on name and theme for returning to hand.
Ninja:
=
(
and
still would work but slightly less so)
Ninja could be Ranged and not be OP.