Spit
Bigger is usually better. A bigger car can fit more people, a bigger gun can fire bigger bullets, a bigger and fatter bank account… Well you know what that means.
In mecha terms, it is usually that way as well. But not always.
The Terrasaur is stupidly big. It swings a heavy punch and it packs a ridiculous amount of firepower. It was as deadly as it was large.
But one thing it was lacking in is of course in movement speed and agility.
True, I did modify it in such a way that its speed and agility weren't weaknesses which other people could take advantage of anymore. But it was not exactly the Terrasaur's strong point either.
It could go fast, but it wasn't the fastest. It could turn at the drop of a hat, but it was a hat that drops rather slowly so it wasn't that awesome.
My secret modification was to simply create a complete but much smaller Terrasaur within the existing Terrasaur.