Well, I do say. It seems I'm gonna be that guy.
So, here are my thoughts on the MU
This MU is boring. Yes, boring. It's slow, and boring. From a neutral position, Lucas will work on getting close to Yoshi to do his combo things, and Yoshi will work on tacking on damage with eggs or messing up his approaches and punishing. If both characters play as carefully as possible, this MU will take a long, long time.
Each character has punishes that wreck the other character's mistakes. The good thing about this is, we force Lucas to approach, meaning we have an easier time punishing. We have kill set ups out of the CG and damage out of it. It also gives us a positional advantage, meaning the match will actually not be boring for once. Nearly all of Lucas's approaches can be punished with a pivot grab or an usmash. Also, don't get anxious for the kill. A whiffed smash could get you killed in turn.
It's pretty hard to gimp a Lucas. They can just wavezap and Magnet Pull to recover, giving immense vertical height and horizontal distance. It's pretty quick as well. We shouldn't be getting gimped much either.
Lucas kills very early. He can set up an fsmash with a dair > dtilt lock > Fsmash. So tech the dair. Usmash hurts too, so be sure not to do anything that leaves you open to get fsmashed. Dsmash lasts a long time, don't get anxious to spot dodge it. Lucas really shouldn't be killing us early on unless you mess up.
Lucas can't really approach safely. Just "camp" intelligently and it's easy. He can wavebounce PKF at midrange, though that doesn't really help him approach since he's pushed back. All it really does is stop a punish. If you get hit, it's not too hard to recover from it if you're at low percents. Higher percents it gives him a better chance of approaching since you're in the air and need to recover.
tl;dr: Boring MU. Massive campfest. Don't get punished. Yoshi's advantage.
Fun Fact: Me and Pink Fresh WiFi'd and it took ~6 minutes for the first stock to be taken. Booooooooooooooooooooooring.