You do realize that being a super/captain multiclass means you end with the Cumbersome penalty (read:no immediate actions) in either form that makes adjacent enemies count you as flatfooted and also automatically confirm their crits, right?
So yes, pretty big robot for relatively cheap, but if enemies get close they're gonna hurt you a lot as they aim at your vulnerable points for critical damage.
Anyway added options for both multiclass super/captain and super size upgrades+transform that allow them to have different sizes because
magic SUPER SCIENCE!
Also, edited in RD's transport version, thanks!
Nature's Oath: At 15th level 1/day, if you would die or your mecha be destroyed while in a location with natural vegetation, you can have trees and vines grow to repair your body and machine. You and your mecha recover all HP and remove all non-instantaneous ill effects from themselves, and can keep acting normally while you remain within 10 miles of the location that brought you back to life. If you go further away, or all the vegetation inside the radius is destroyed, you die.
This replaces the bonus feat a Super Pilot usually gains at 15th level.
I think something is missing to allow you to move more than 10 miles from this place, ever, without dying and making it questionably useful as a replacement feature (sure, I can keep fighting for the one battle... in the right environment, and if we have to move on I drop dead?)
Very well, added option of ending the oath.
Also rewording, because it currently kills you if you move too far away and your mecha was the one broken.
That's not a bug, it's a feature of being a tree-hugging elf.