Shield.

[Triple J]

This has probably been brought up before - in the Runouw forums, but what about a shield for the player? Those enemies don't stand as much of a chance if you use a shield to block, or even counter their attacks!
Of course, there should be some boundaries to avoid any overpowering:
Idea 1: Some shields may break.
Idea 2: Sometimes you lose hold of your shield, and it may go flying when you block an attack. Go retrieve it!
Idea 3: Certain shields only block certain means of attacking.
Idea 4: Shields have specific weaknesses.

[Cordelia]

I've brought this up in a few of my posts on the Runouw forums regarding some sort of defensive options for the player. A shield would certainly be a nice item for the player to have, but given the fact that this is a 2D game, the shield might be too overpowered. I think a dodge would serve as a much better defensive option. Something akin to a backdash.

[AwesomeJRFD]

It wouldn't be too OP if it counted as a weapon like handcuffs and you have to hold right-click to use it. It should also probably have a limit to how long it can be active, the player can't attack or jump as high while it's active, and it maybe slows down the player while active as well.