I hear a certain My IGN moderator has challenged us to make a blog about our favorite pant-less characters... challenge accepted! 
Here's Yoshi! He made his first debut in Super Mario World as a mountable sidekick, but his presence has expanded greatly since then! Not to mention, he's cute to boot! <3
As you can also see, Yoshi does not wear pants, and he does just about everything without ever having the need to! From his platforming adventures with Mario to sports, smashing, and racing, he does it all without a single pair of pants in sight. Unlike the Mario Brothers, he ground-pounds without any pants; what a bunch of jokers! 
There's also this...
Seriously, though, Yoshi is perhaps my favorite character from the series. Every time I see him appear, I always get this "best pal" vibe from him, and it's nothing short of describing the green dino; he really is such a reliable and loyal character! Even though he just barely met the young plumber-to-be, Yoshi went out of his way to save his brother and return him to the stork! He even helps out again once he reunites with Mario and onwards! 
With his wide array of powers, Yoshi is a force not to be denied! His flutter jumps make large gaps accessible, and his long-reaching tongue can propel him in places he couldn't reach as well as grabbing his opponents for him to swallow down, which turns them into eggs that is used as ammunition. A head-butt or ground-pound from him will definitely put enemies in a world of hurt!
In most of the spin-off games he's in, he tends to offer some great balance with a focus of speed and or accuracy. Regardless, he is nearly always my first pick in the roster because he's just so damn cute! XD