Chaos Emerald

A Chaos Emerald is a powerful gem found in the Sonic the Hedgehog series that has made several appearances in crossovers with the Mario franchise. The Chaos Emeralds hold large amounts of power that can be used in various ways, and allow characters like Sonic to transform into their Super State when all seven are collected. In crossover appearances, Chaos Emeralds usually appear as items in Dream Events in the Mario & Sonic series, as well as making smaller cameo appearances in the Super Smash Bros. series.

Mario & Sonic at the Olympic Games
In the Wii version of Mario & Sonic at the Olympic Games, the Chaos Emerald appears in Dream Race as an item that is most frequently obtained when the player is in fourth place. When used, the player becomes invincible and gains a speed boost, as well as stunning all of the other characters and causing them to lose speed. In the Nintendo DS version, the Chaos Emerald appears in the Dream Basketball event, where it can be used to cause either the other characters' baskets to move faster or a Boo to block one of the baskets. In Dream Long Jump, the Chaos Emerald can be used to create a strong headwind that affects all of the players.

Mario & Sonic at the Olympic Winter Games
Chaos Emeralds appear again in the Wii version of Mario & Sonic at the Olympic Winter Games in the Sonic World routine in Dream Figure Skating. Three are collected during the first segment, and the other four are collected during the second one. In the final segment, they are used by the characters to defeat Perfect Chaos.

In the Nintendo DS version, Chaos Emeralds appear as items in Ski Cross Racing and Extreme Snowboarding, where they stun all of the characters in front of the opponents and remove their items, while in Rocket Ski Jumping, using a Chaos Emerald causes all of the other characters to be struck with lightning, making them lose speed and altitude. In Fever Hockey, the Chaos Emerald item causes tokens to appear on the rink that strike opponents with lightning and knock them down when collected, and in Ski Shooting, using a Chaos Emerald stuns all of the opponents and prevents them being able to shoot for a short amount of time. Chaos Emeralds are also used in Ultimate Figure Skating to indicate areas on the rink during the routine where the player can perform spins and defeat enemies.

Mario & Sonic at the London 2012 Olympic Games
Chaos Emeralds also appear as an item in London Party mode in the Wii version of Mario & Sonic at the London 2012 Olympic Games, where they can be collected from the ? Balloons that appear around London. When used, they stun the players' opponents for a few seconds.

Mario & Sonic at the Rio 2016 Olympic Games
In the Wii U version of Mario & Sonic at the Rio 2016 Olympic Games, Chaos Emeralds appear as an item in Duel Rugby Sevens, where they knock over opponents in a circular radius of the player when used and score them Duel Points. In the Nintendo 3DS version, Chaos Emeralds appear as an item in Boxing Plus, where they will fill the character's Special Punch gauge faster for a short amount of time.

Super Smash Bros. series
In the Super Smash Bros. series, the Chaos Emeralds appears during Sonic's Final Smash, Super Sonic. Once the Smash Ball is broken open, the Chaos Emeralds instantly appear around Sonic, causing him to transform. The Chaos Emeralds also appear on the Trophies for the Final Smash in Super Smash Bros. Brawl and Super Smash Bros. for Wii U. Also in these games, the blue Chaos Emerald appears in one of Sonic's victory poses if he wins a match. In Super Smash Bros. Ultimate, Shadow holds a green Chaos Emerald when he appears as an Assist Trophy.