Though Super Mario 3D World was a lot like Super Mario 3D Land, it was hard to complain about another adventure with more levels and brand-new power-ups. Besides the overused Cat Mario suit no one asked for, the Double Cherry item never wore out its welcome. Simply nabbing the Double Cherry in a level pops out a clone of Mario, one that mirrors the player's every move. It lead to some neat puzzle-solving situations, and also unbridled chaos when combined with other powers.
Unfortunately, your clones vanish once you finish the level, so you can't storm Bowser's castle with an army of dead-eyed Italian stereotypes. But it's fun while it lasts, and it never slows down gameplay; if one of your clones meets an unfortunate end, you can still continue on without them. But what happens if the Prime Mario dies?
Nothing. Nothing happens. The clone continues on in Mario's place, even after the original is wiped out of existence. Despite being born seconds ago, this new Mario takes over Prime Mario's life. No one notices or cares that Mario died and was usurped by a soulless doppelganger. The Double Cherry is the Waluigi of power-ups.
Yoshi is one of the last major additions to the Mario canon, and he's endured for years. It's always a treat to see Yoshi pop up; he's like a power-up that happens to also love you unconditionally.
But that's sort of the problem. Despite his sentience, Yoshi has always been treated like an expendable power-up in the mainline Mario series. From the moment he's born, Yoshi is used as a tool to meet an end. I'm not even exaggerating. The first time you meet Yoshi in Super Mario World, he hatches and you start riding him in seconds.
Luigi can't be bothered with reading anything poor Yoshi might have to say, because he's already busy punching his new friend in the face to get his tongue to come out. Nobody sees Yoshi and says "Wow, a talking dinosaur hatched out of this egg as a fully-formed adult! It's a miracle of nature!" Instead, the Mario Bros. first thought about Yoshi is how best to enslave him for their own purposes.
It's even sadder when you realize that the Yoshi species have evolved to deal with this reality -- they're born with built-in boots for the endless miles they'll have to walk and a saddle for their tormentor to sit in. You know, just so Mario is extra comfy for a few minutes before he ditches Yoshi down a bottomless pit to get some extra jump height.
To be fair, some Yoshis are actually born babies. They don't have it any better.
In order to grow, Mario force-feeds this comatose newborn constantly, gobbling several times its own weight in seconds. This will happen until the Baby Yoshi grows into an adult, after which it is immediately enslaved. But in the newer games, Baby Yoshis are never seen growing up -- so they're basically just used as a weapon, a living garbage disposal by Mario and company.
All in all, it's a pretty deplorable way to treat the species that saved your ass as a kid.
They probably should have eaten Baby Mario and pooped him out as an egg right then and there. Would've saved themselves a lot of trouble.