Oken

Auras: Auras increase player attack and defense. Oken can store up to 3 auras and he can consume one of them to perform a powerful attack. Detaled description is here.

Dark auras: Dark auras consume one of  the stored auras. Detaled description is here.

Walls: Walls let the player slide down using the wall slide ability. While wall sliding he can jump to climp up the wall. This mechanic is very similar to the one found in classical megaman games. It is possible to create vertical areas without ground. Also making use of this ability is possible to create zones of pilars where the player have to wall jump from one to the next.

Water: Oken is unable to swim so water shouldn't be deep. The water areas will slow down the player making it difficult to move. If the player is one of this areas, he will be faster jumping than running. This should be used to create interesting gameplay scenarios.

Holes: The ground can have holes that will provoque instant player death. This should be restricted to a minimum and only be used if the level really needs it. Water areas are prefered to holes.

Spikes: Levels will be populated with spike plants that will hurt the player. This is perfect for creating evade scenarios for the player.

Poisoned spikes: This kind of spikes will hurt the player and also will poison him so that he will continue to lose health for a short amount of time. The player cannot die from this effect so poison will never put the player health below 1hp.

Dark aura spikes: This kind of spike will hurt the player and also will consume one of his auras.

Slippery area:  This kind of area prevents Oken from doing his wall slide ability. 

Humanoid enemies: This kind of enemy will have an standard attack combo and possibly special abilities. This kind of enemy can wear an armor.

Non-humanoid enemies: This kind of enemy will be generally smaller than standard humanoid enemies and will only have special abilities/attacks only. Examples include: spiders, bats, serpents, giant monsters, etc.

Bosses: This kind of special enemy does not have any kind of general design rule.

Enemy Bullets: Certain types of enemies will fire some kind of bullets (like acid and arrows). If Oken is hit by this projectiles he will loose health. 

Enemy armor: Humanoid enemies can wear armor. Armored enemies are inmune to knockback.

Gates: Parts of the level that will not be accessible (stopping the player from advancing) until certain conditions are met like defeating certain number of enemies or recovering a key.