Any Ideas on how to make a "shield surfing" system like legend of Zelda?

Hey, I’ve been looking for this on google but can’t find anything. If anyone knows a tutorial, that would be great. Otherwise, any ideas on how to get it done?
My first idea was setting the walkable slope angle to 0, so it starts “falling” on any inclination, but it can only go downwards, it doesn’t matter how much momentum you gain. You also lose all your momentum when reaching a flat floor (because angle 0, so it stops falling). Any other ideas?