Hi, I looked around to see if anyone's reported this but it doesn't look like it so I figured I would put it here (if I missed this then I apologize). Not sure if it's viable for the any% route but I feel like it might be worth posting anyways (could have an application in other categories, maybe?); the short version of it is that you can get a really strong "sword" on Deku's B button (i was able to get a similar effect on Zora's punches, but haven't been able to replicate it yet).
- Get mask storage with Deku and climb onto Epona
- after transforming, remove the mask from your items to turn human, and climb off Epona
- Human link now has Deku Nuts on his B button. When you transform into Deku, you have an invisible, fully functional (sans crouchstab) sword on B. If you have never picked up Deku Nuts, it will even persist through flying; if you have picked up Deku Nuts, it will be overwritten (presumably because it sets your B button to nuts during flight)
You can get back your sword on Human by repeating the process, and it does not get rid of the sword on Deku.
The thing that might make it worthwhile is that it seems to have the same strength as the GFS (it one-shots Dinolfos). It does not persist through saving, however (which zora punches did, but again, can't figure out how exactly I managed that one).
My knowledge of MM3D speedrunning is pretty small, but I hope this information is useful.