Dark Shadow

Dark Shadow is a Quirk used by Fumikage Tokoyami.

Description
This Quirk allows Fumikage to host a "shadow like-monster" that he can materialize from his body and contract it back into his body freely. Fumikage can use for a number of purposes, such as attack, defense and support. This shadow has shown to be sentient and has an energy limit, that when it runs out, the shadow will retract back into Fumikage. According to Mezou, Fumikage's negative emotions (such as regret and indignation) probably intensifies Dark Shadow, making it more unruly and possibly making Dark Shadow stronger as a result, albeit at the cost of Fumikage losing control.

The personality, strength, defense and control of the shadow-like monster depends on darkness and light:

Under the power of light, Dark Shadow is weaker but despite this, it still has extraordinary defensive skills as it was able to completely block Katsuki's Explosion without suffering any damage as well as defend against Denki's electricity (despite having weaknesses to both of them due to the light they produce). Dark Shadow's personality under light is docile, allowing Fumikage to control it with ease.

Under the power of darkness, Dark Shadow becomes far larger and ferocious, and as a result far more powerful. One of Dark Shadow's claws was able to rip through multiple trees with ease when trying to attack Izuku; Dark Shadow's physical strength is immense as it was able to defeat Moonfish, a veteran villain, with a single strike, completely shattering his sturdy weapon-like teeth in the process. Dark Shadow's personality completely changes when surrounded by darkness, becoming more unruly, vicious and attacks indiscriminately, striking anything that moves or makes sound. It appears keeping Dark Shadow under control during the night where darkness is most prominent is a great struggle for Fumikage as it requires all his focus. Once Fumikage loses control, Dark Shadow starts enveloping Fumikage's body with its darkness and takes control over its host, with Fumikage slowly becoming immobile both physically and mentally. After taking over Fumikage, Dark Shadow uses its immobile host to move around.