I tried that one trick where you press grab and down on the same frame, but fat fingered the taunt key and pressed grab and taunt on the same frame instead. Could be useful if you can use this with super-taunts too since it would skip the animation but still screen-wipe.

From my testing, this only works when running at speeds below mach 3 (without the yellow dash effect in front of Peppino). You also can't skip the parry animation (I think if you do end up parrying then you pressed taunt early; normally I would end up grabbing into the enemy and either doing a spinning attack or getting hurt by it depending on my positioning). If you attempt to supertaunt doing this, the warped taunt sfx will play as if you supertaunted, but Peppino will uppercut, no screen clearing will happen, and the supertaunt won't be "spent" so you will still have the electric effects and can use it afterwards regardless.

I also found that if you uppercut within maybe 1 frame after taunting (I don't think this one is actually frame perfect like the grab variant is), it will similarly skip the taunt animation and uppercut. I don't know if this was already known, but I imagine someone has seen it before when experimenting with taunt updoors. I don't think this uppercut taunt skip works with a supertaunt, but it was hard for me to test thoroughly as I didn't use debug mode.