Skulk

Skulk is an evasion ability introduced in Shadows over Innistrad.

Description
A creature with the keyword skulk can't be blocked by any creature with greater power.

Skulk was designed to be an evasion mechanic that kept you from making your unblockable creature much bigger with Auras and Equipment. It was designed in an attempt to create an evergreen keyword shared between Blue and Black, but it didn't end up working out. It was both more complex to use than the designers thought and had far less design space than they had anticipated. It was only interesting on low-power creatures and didn't mix well with a lot of other creature abilities.