Hello everyone, I'd need your help on that case :

Nick has a morph into play, with an equipment attached to it. He puts the artifact under his morph creature. Nick attacks Matthew with the Morph. Matthew takes a moment to ponder the situation, then lift up the Morphed creature, turning it of about 90°, hence having a clear sight of the face-down card.

“Judge !
- I was only checking the equipment…I didn't pay attention to the morph card.”

What should be done ?

Investigate the situation with a few more questions to determine if you believe the player. Assuming that the player is being truthful, issue a warning for Looking at Extra Cards and remind him to be more careful in the future, perhaps just asking his opponent if he can see the equipment.

Originally posted by John Brian McCarthy:

Investigate the situation with a few more questions to determine if you believe the player. Assuming that the player is being truthful, issue a warning for Looking at Extra Cards and remind him to be more careful in the future, perhaps just asking his opponent if he can see the equipment.

Very much so this. Do note that there's no “fix” to this situation if you issue the Looking at Extra Cards penalty, as that's a question you may receive from the opponent if he asks why the other player gets to know the identity of his Morph without any fix or something beyond a Warning.

I had this exact same thing happen during a Sunday Super Series but NAP was trying to see what Cloudform gave the manifest it was attached to. It is one of those things situations where there's nothing you can do but give the warning. Much like accidentally flipping over cards while shuffling an opponent's deck can tell you what deck they are playing, if someone starts wracking up warnings for this specific thing they're likely to get into trouble.

One thing I advise saying here is “In the future, please ask your opponents to show you their cards instead of just grabbing them yourself.”