Mill Rule 701.17 Glossary

To mill a number of cards, a player puts that many cards from the top of their library into their graveyard. See rule 701.17.
Skulk Rule 702.118 Glossary

A keyword ability that restricts how a creature may be blocked. See rule 702.118, “Skulk.”
Transform Rule 701.27 Glossary

To turn a double-faced card so its other face is up. See rule 701.27, “Transform.”

Rulings (3)

April 8, 2016 Wizards of the Coast
A sorcery can't be put onto the battlefield and a permanent can't transform into a sorcery. If an effect exiles Persistent Nightmare and then instructs you to return it to the battlefield, it remains face up in exile (unless that effect instructs you to put it onto the battlefield transformed, in which case it returns as Persistent Nightmare). If an effect instructs you to transform Persistent Nightmare, the instruction is ignored.
April 8, 2016 Wizards of the Coast
If you cause a creature to have 0 power or less, use the actual value (which may be negative) to determine whether it can block or be blocked. A creature with skulk and 0 or less power most likely won't be blocked, but it won't deal combat damage and won't trigger any abilities that trigger when combat damage is dealt.
April 8, 2016 Wizards of the Coast
Skulk matters only as blockers are chosen. Modifying either creature's power after blockers are chosen won't cause the attacking creature to become unblocked.

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