Specials

The "Special" button can do one of 3 things chosen at the character select screen.

Parry

Press light when selecting your character to choose the parry special. Pressing the special button will put your character into a parry state.

If they're attacked while in this state, the attacker will be stunned instead. After 30 frames if your character is not hit then they will be stunned.

Offensive Tag

Press medium when selecting your character to choose the offensive tag special. Press the special button to perform an assist as your point character, and then immediately tag them out.

This is useful because it lets you tag in as your assist character without leaving your point vulnerable.

UBHOD

By pressing heavy when selecting your character you'll choose the UBHOD special. Press the special button while above half meter to enter UBHOD, and press it again at any time to leave UBHOD.

This helps you control when you enter and leave UBHOD which can be very powerful.