Hero Core - Official game guide|
Introduction - Basics - Enemies - Bosses - Trivia
Normal - Hard - Annihilation - Boss Rush - Hero Forever
Various tidbits about the game that didn't fit on the other pages.
Hero Core was made in three months starting February 2009, five months after Iji's original release. The music slowed the project down however, so I continued polishing and testing the game, adding things like the boss hint system and translation support. Some of the original plans for the game were SNES-like graphics and four basic weapons - I didn't think color graphics would fit the game, and it would've increased the development time by a lot. I also felt that needing many different kinds of weapons to enter certain areas of the asteroid would be too limiting and confusing, so I decided on a more free-roaming approach. Finally, I didn't want a repeat of Iji or Metroid, where dying was extremely costly; I figured there was no reason not to keep the player's progress upon dying. I was also bothered by the long travel distances of Castlevania: Symphony of the Night, hence the warp-anywhere mechanic and cramped game world. I wanted the game to help and encourage the player as much as possible.
If you destroy all the spheres surrounding a Mode, the next time it wants to fire lasers, a question mark will instead appear above it. The Elite boss, much like Hero, cannot fire Expel with only 1 HP left - a question mark will appear above it as well. Finally, while it's very hard to do, if you destroy all of a Warp eidolon's guns it'll become more aggressive and start ramming you with its body.
Behind the hydra
If you fly behind the heads of the Plasma Hydra, the guns on its back will start firing a lot of bullets.
The idea for the Eliminator was a combination of Cactus's suggestion about a roaming enemy, the SA-X in Metroid Fusion, and some of the earlier plans for the game where every boss machine in the base was free-roaming. When a friend saw me playing and pressing the debug key to destroy all enemies upon entering a room, he thought the effect would be neat if used in the game somewhere, hence why everything explodes when the Eliminator appears.
One of the computer rooms on Hard difficulty (underneath Plasma Hydra) is modeled after the item room in the original Metroid. The Old Base zone is a copy of Level 1 from the first Hero - on Hard difficulty the zone is upside-down. Also, the entrance to the secret in the Old Base on Hard mode is in the same location as the Inner Prey secret in Iji. The ruined Generator holder found in the Old base also has the old design from the first game.
While the entire Annihilation difficulty takes place on a certain spaceship mentioned in Iji, the final alien computer also contains morse code for "the Zentraidon", another Iji reference.
Sharte and missingno
To avoid confusion with enemy types and spawners during development, the Spawner enemy is actually called Sharte, randomly named after an animated puppet in Rhapsody: A Musical Adventure. When you face the Eliminator in the Boss Rush, there's also an invisible, invincible enemy in the bottom right corner of the room called missingno, named after a glitch in Pokemon. Its only purpose is to keep the door shut, as the Eliminator normally cannot appear in a room with a door. Missingno has the sprite of Hero's regular bullets.
The small flies found fluttering around, mostly in the Old Base zone, will light up if you shoot at them. The Blade also swats them to the ground.
Hero Forever actually has a "kill screen" - if you reach level 999, the entire level will be completely empty and silent. There is no way to progress from this level.
The "Neo joke translation" was made available in version 1.4 of the game, and is unlocked by pressing up, up, down, down, left, right, left, right on the title screen. It's just an in-joke with a friend.