Energy Cores are objects that first appeared in Shadow the Hedgehog. They are glowing energy orbs that work as power-ups and are used for various actions.
Shadow the Hedgehog
Energy Cores first appeared in Shadow the Hedgehog. In this game, it is used for charging either the Hero Gauge or Dark Gauge. The Energy Cores for filling the Hero Gauge are blue and the Energy Cores for filling the Dark Gauge are purple. They are present in every stage in the game, but the purple cores are easier to find.
In the console/PC version of Sonic Generations, the Energy Orbs play an important role in the rival battle against Shadow. Here, both Sonic and Shadow race against each other to collect Energy Cores which flow down the course at high speeds. When a character collects a Energy Core, another will appear further down the course. For the player, the only way to beat Shadow is to collect enough Energy Cores (which is two in normal battle, three in hard mode) and use them properly.
Once either character collect a set amount of Energy Cores (two on normal mode and three on hard mode), he will execute a special attack at the opponent. However, the attack manifests in different ways for Sonic and Shadow:
Shadow: Shadow will launch a salvo of Chaos Spears onto the ground. Trying to reach Sonic for another blow, Shadow will warp himself above the ground instantly from both directions. As this state fades out, Shadow charges up a more powerful Chaos Spear and throws it at Sonic as his final blow.
Sonic: Sonic automatically performs a purple and empowered version of the Boost. While racing at Boost speed, Sonic can pierce Meteorites and shatter them into three shards that are flung directly into Shadow and decrease his speed. As Sonic reaches Shadow, he can bypass the protection of Shadow's Boost and damage him until Shadow's Ring count reaches zero or Sonic's Boost Gauge runs out
As soon as the character's special move ends, they have to collect another set of Energy Cores to perform it again.