I could fully rewrite it to explain how it works, but I just woke up from a nap and I'm too tired to do that.

So, I've got about three options and if I sound grumpy it's because I just woke up.
[list]
[*]Erde dies right now from the force of the impact, and then you have nobody of comparable power and size to fight MegaMechDude.[/*]

[*]Erde's rock drops to the ground and then he reforms a body of equal size to the mech and you have an even fight with Erde.[/*]

[*]Erde goes flying off into the distance, well out of your way, and problem number one (Where you have nobody of comparable size to fight.) surfaces again. Until he comes back with 2 miles worth of minerals and a very bad reaction to being launched into the distance.[/*][/list]