Rightside Down Secret
From Lumapedia
Advanced
0:00 - Intro Cutscenes are skipped RTA.
0:10 - To conserve momentum for this single jump, hold neutral until after you've pressed A. Try to jump immediately as Mario lands on the platform.
0:16 - I switch to up-right as soon as Mario runs over the intersection of the two diamonds on the ground, then immediately Long Jump.
0:36 - Try not to throw these fireballs too quickly as Mario may throw them in the wrong directions. Hitting Z between each throw allows you to turn and throw a new one faster.
2P Notes
2P can be used to break a couple boxes for you, but isn't much faster without the use of TAS tools. It can also be used as a back up for any missed boxes. For an example that does both of these things, see: Rightside Down Box Game 2P