When in doubt, watch the TAS: http://tasvideos.org/3968S.html In particular, here's the timestamp:

Obviously boosts aren't super possible here, but of note: You both are starting with a slope jump, which is a higher base speed -- you're preserving that by bouncing on the goomba, which is very similar to the TAS's W3 Lair:

IIRC the main issue with pulling this off consistently is the jump timing -- if you have to adjust left to land on the goomba, then you're not saving any time.

100% what darkid is saying. Wanna add that it's somewhat known (I knew about it) and I've pulled it off in some practice runs (never in a record run I think), but if you jump too late you end up in the pit or have to adjust in-air and you mostly lose time. It's a risk/reward type of situation. There are many other similar small improvements that can be done to the current route that are mostly not done because messing it up loses so much more than what's gained from getting it right.