I find this quite UP when comparing it to Rage pot.
Rage pot takes hp away for the same effect, but is more profitable.
This just gives 5 atk for the cost of single creature in 2 turns and only gives Demon +1.
I suggest for upped increasing it to +2 so then its worth its upgrading cost.
I Personally dislike creature cards that only offer +1 cost changes for very minor atk/hp increase for 1500 electrum, too expensive for such a minor effect, It would be the last thing I upgrade in my deck after upgrading other important cards for maximum deck potential, since they can still potentially be killed by the same effects which were once a danger
to the creature previously.
My suggestions are:
Make it worth its upgrade; for upped, change the stat adding effect to +2
or
Make the upped ability only cost 1
.