[section=Good ending]This one is well known. To get the good ending, transform into a Hybrid, a Centurion and an Azure Dragon. Contrary to what some walkthroughs claim, the order does not matter. The fourth crystal will now be black and transform you into the secret Dark Angel form. Beat the game with it to get the good ending.

[section=Upgraded transformations]Not much of a secret. If you collect three crystals of one type, Abel will transform into a stronger version of his current form.

[section=Mapselect]At the title screen, press select 15 times and then press start to enter the Options screen. There should now be a secret MAPSELECT option which you can use to select the stage you want to start the game from.

[section=Infinite health - Lava level]There is a health orb at the end of the first screen of the lava level. Since it respawns every time you reenter the screen, you can use it to regain as much health as you like. This is useful if you really need to heal up before taking on the Salamander, although it may not be so useful for speedrunning.

[section=Hidden health orb]Near the end of the lava level, there is a health orb hidden right above the doorway to Beelzebub. Useful if you are low on health and don't want to waste time eating pixies during the boss rush.

[section=Infinite health from bushes]Normally, only two Dryads/Pixies will pop out of each bush in level 2 and 6. However, if the bush leaves your field of view and you revisit it, two more Dryads/Pixies will pop out. You can repeat this process as many times as you want. Useful if you need to restore your health but not really useful for speedrunning.