The Engine Core is a big machine attached to the back of armored trains. It has a blue core in the center with several rings of red and black metal surrounding it and the core itself is attached to a numbers of cables that feed its energy into the Bull Train.
The Engine Cores only appear in Bullet Station. In gameplay, they serve as a way for the player to exit the transport tunnel sections in Bullet Station. When destroying an Engine Core, it will create a massive explosion that will destroy the Bull Train and additionally send the player flying out of the transport tunnel to the next section in the Stage. The Engine Core can only be destroyed by an attack from Power Formation.
- Sonic Heroes: Prima's Official Strategy Guide, pg. 87