Such cloaks are in high demand both by assassins and by those who fear them.

Equipped creature can't be blocked and has shroud. (It can't be the target of spells or abilities.)
Equip {2}

Whispersilk Cloak

Duskmourn: House of Horror Commander

Secret Lair Drop

"It bends the light somehow, rendering it—and its wearer—functionally invisible. I never would have found it if I hadn't tripped over it!"
—Quintorius Kand, research notes

The Lost Caverns of Ixalan Commander

"Are these magic cloaks?" asked Pippin.
"I do not know what you mean by that," answered the leader of the Elves.

Tales of Middle-earth Commander