"...or I make a ladder?"

Mat thinks that makes a bit more sense.

"Trust me, I'm already terribly impressed, you don't need to show off for me."

It takes more effort than normal, but he manifests a sturdy looking ladder. That will hopefully remain in existence. But he trusts Jesper to be fast - he knows the other fellow is remarkably quick when need be.

This certainly counts as 'need be'.