Ultimate Challenge 3 in

This is done in 1.0, but works just as well on the current version.

You can also slightly adjust the strategy for a 100% consistent route to beat UC3 (it not 100% consistent on 1.0 due to some differences in how reaction shots work):
In turn 1 shoot with Luigi before shooting with Rabbid Mario (but after the Magnet Dance)
And in turn 4 move RM one tile further to the left and jump with Luigi behind the cover block to the upper left and then end turn
In turn 5 use Luigi's sentry on the Ziggy on the isolated platform and you can now freely walk to the goal zone

But we are not here to discuss consistent strategies, instead let's focus on the Speedrun side of things.
There is a very interesting reason I did this on 1.0:
For some reason on current patch in turn 3 half the enemies spawn before the tornado and half after, which does not happen on 1.0. Therefore 1.0 is about 5 seconds faster.
But due to the differences in reaction shots you have to crit with the second Steely Stare shot on 1.0, because Luigi would get a third shot to finish the job otherwise (contrary to current patch) making 1.0 less consistent.

There are so many differences between 1.0 and current patch, it almost feels like a completely new game lol.

The turn 1 strat is fairly slow compared to some other routes, however that sacrifice is being taken to ensure that no enemies spawn on turn 2, which makes up for that time loss and even ends up saving time with the additional 5 seconds gained in 1.0.
The 'second wave' spawns if anything in your team, including sentries, crosses an invisible plane, so we can't go too far in turn 1 or use a sentry to kill the furthest enemies.

Every enemy that spawns in UC3 (except for calavera who always spawns on turn 4) works that way. You may know there is a glitch to prevent enemies from spawning, whose spawn condition is the team crossing a certain plane. It would save a lot of time to have that glitch here too, but so far no way has been found to do it outside of 3-4-1. Maybe something to look at in the future.

Till then I hope you enjoy the run!