Mystical Space Typhoon vs. Dark World Lightning

My opponent had 1 face down S/T on his field, that's it.

I had Grapha, Overlord of Dark World.

I use Dark World Lightning to destroy the face down, and he chains it, activating Mystical Space Typhoon.

He said since he chained it, I can't discard. But I told him he has to have a legitimate target for MST for him to activate it. He had none.

So, can I get some clarification? Thanks in advance.

MST requires a spell card on the field. Your Dark World Lightning is on the field, so they can chain MST to destroy DWL, though this does not negate it.

HOWEVER: DWL requires it's target to be face-down at resolution. Because MST has been activated and is now Face-Up, DWL cannot destroy it, and as a result, it cannot discard a card.

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As that ponies said,
DARK World lightning only work if you destroy FACE DOWN.

the rest are same / already explained

Pretty much same as nobleman of extermination

kangtuji wrote:
As that ponies said,
DARK World lightning only work if you destroy FACE DOWN.

I'm sorry, I'm just going to say something to avoid confusion.
DWL does not work if the card being targeted is face-up at resolution.
For example:
>Activate DWL
>Opponent chains the targeted Ultimate Offering
>DWL does not destroy Offering because Offering is no longer face-down.

Just trying to avoid confusion.