As Kuroaitou already said, i think that the variable ability cost doesn't work.
Think about the gameplay:
You click on your "Soul eater" to devour a creature. How many quanta you spend?
And THEN you click on a target.
In Elements, when you click on the creature to activate the ability, you spend quanta. Not after you selected the target.
Suggestion:
"1
: Devour target creature (any hp) and gain +1/+1
Increase ability cost by 1
"
or
"1
: Devour target creature (any hp) and gain +1/+1
Increase ability cost by 2
"