Jack-O's "Defend Command" action parries any move that comes into contact with her Servants while it is active.

She can do this while holding a Servant above her head, using 236[P]>S.

In any situation where a foe makes contact with this Shield, they enter a Guard Break state.

In this Guard Break state, they're vulnerable to Jack-O's Overdrive, Forever Elysion Driver. This situation is unblockable.

This spreadsheet has recorded (almost) every move in the game and their interaction with Jack-O's shield, but only while she's holding the Servant above her.

I didn't test many Aerial moves, only specific ones I thought were of note.

It's generally safe to assume air moves will make contact with the Servant before Jack-O'.

Jack-O' has an animation where she leans forward a bit to do the command, but the Shield lasts a little longer than that.

This animation changes her hurtbox a little bit, so some moves might only work late in the Shield's active frames. Those will be noted.

A move might be marked "YES" or "NO," but have specific situations where an exception can occur. The exceptions will be noted.

Any egregious examples of a move having a specific behavior that prevents it from being reliably Shielded will not be noted "YES" or "NO," instead skipping straight to the explanation.

Just because a move CAN be Shielded doesn't mean it SHOULD. I'm not making any strategic calls for you here, but rather giving you the tools to do so yourself.

If you decide to run at every character in the game and try to shield their c.S, leave me out of it!

The opponent's reaction to projectile shielding is proximity based. If you're nearby them when you parry a projectile, they'll enter Guard Break state. If you're far away, nothing happens.

Eddie and Jack-O's Servants function the same way.

If there any problems with this document or you find something cool you want added, talk to @UltVictory :)