Growing over time might just be the best way. I would suggest that you tie total health AND energy capacity to size. The infinite energy capacity seems a bit odd to me.

And if we are going with size over time, would you mind growing me length-wise instead of in diameter? 

Anyway, it's time to go balls out.

>Evolve Speed 3
>Evolve Venomous Tail Stinger. 
>Keep heading left, towards the plants I guess.