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 the shadow-like monster for a number of purposes, such as attack, defense and support. This shadow-like monster has shown to be sentient. The shadow-like monster has an energy limit and when it runs out, the shadow like monster 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 and was able to block Denki's electricity (despite having weaknesses to 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 with one strike, a veteran villain and completely shatter 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.