0, breaks the game, or just does 0 damage
1 does 4 damage
2 does an average of (8+2)/2 = 5
3 does an average of (12 + 3 + 3)/3 = 6
4 does an average of (16 + 4 + 4 + 4)/4 = 7
5 does an average of (20 + 5 + 5 + 5 + 5)/5 = 8
ambiguous case (algebra)
x does an average of 4x(1/x)+x(1-1/x) = 4+x -1 = x + 3
the mechanic is very nice, but it isn't worth the steep cost.
Im not an expert in this, but I suggest 3|3 for cost
Next, one reason people have been having problems with creating fire is that the entire element is pretty comprehensive, and doesn't really need a new creature so much. Consider putting this in entropy or gravity (change name to critical hit)