Yoshi

Yoshi is a green dinosaur-like creature from the Super Mario franchise. He has appeared as a cameo in several Metal Gear games.

Metal Gear Solid: The Twin Snakes
Yoshi appears as a cameo along with Mario in the HAL Lab. If you shoot Yoshi he'll scream his name. If you shoot Mario, a "1-Up" sound can be heard and Snake will gain a little bit of health.

Super Smash Bros. Brawl
Yoshi and Snake both appear as characters in this game. During a codec conversation, Snkae says he's interested in cathcing Yoshi and eating him as food.

Metal Gear Solid: Snake Eater 3D
Yoshi appeared at the end of the trailer for this game. He replaces all Kerotans.