Splooshi Splashy
Smash Journeyman
Side 1 doesn't have any invincibility frames, but it DOES have super armor on the Clown Car itself, albeit a rather inconsistent amount of it. It may just be patch placebo, but it seems like Side 1 has more vertical range on its super armor. The most consistent projectiles I've been able to Side 1 through are reflected/enemy Mechakoopas, Trip Saplings, and Banana Peels. If you're looking for a Side B with consistent super armor from frame 1, you'll want Side 3, Grounding Dash. I'd personally run it against folks like Yoshi, Sheik, and Duck Hunt.
There are two major types of hits that can happen to Jr post Up B. Strong hits like Smashes, most aerials, and sweetspotted attacks will allow Jr to get back the Car, provided said Jr player presses R (or the airdodge button) after taking the strong hit. Weak hits like Jab 1, some aerials (Duck Hunt's NAir when sourspotted, for example), and sourspotted will not generate enough force for the R button trick to work. What seperates the strong hits from the weak hits is the amount of knockback said hit causes. The stronger the knockback, the more likely it is for the R button trick to work. The amount of percent Jr has on also seems to affect this, with more moves allowing Jr his Car back the more percent Jr has on.
There are two major types of hits that can happen to Jr post Up B. Strong hits like Smashes, most aerials, and sweetspotted attacks will allow Jr to get back the Car, provided said Jr player presses R (or the airdodge button) after taking the strong hit. Weak hits like Jab 1, some aerials (Duck Hunt's NAir when sourspotted, for example), and sourspotted will not generate enough force for the R button trick to work. What seperates the strong hits from the weak hits is the amount of knockback said hit causes. The stronger the knockback, the more likely it is for the R button trick to work. The amount of percent Jr has on also seems to affect this, with more moves allowing Jr his Car back the more percent Jr has on.