Great idea for a card.
One small note. The average damage works well for creatures that survive for the rest of the game. (The previous creature I used that metric on could kill the opponent before they died) Creatures that don't survive that long need to include the turns where they deal no damage because they are dead into the equation. Also it is typically better to use the value of similar skills to determine the appropriate cost. Skilled creatures tend to be able to get the same value for lower cost because their potential is vulnerable to lobotomy.
So for this card 7|7 is the maximum that this should cost. However it probably should be reduced in cost some.
This card gains +2|0 and -0|1 per turn otherwise known as a free ablaze per turn and "poisoned".
Ablaze [+3], Generate 1 Quanta (free ablaze) [+1], 5<HP<8 [+1] = 5|3-4 quanta for a non "poisoned" one.
I would guess that "poisoned" reduces the cost by 1 more at least for a maximum of 4|3
.