Antimagic Susceptibility. The rug is incapacitated while in the area of an antimagic field. If targeted by dispel magic, the rug must succeed on a Constitution saving throw against the caster's spell save DC or fall unconscious for 1 minute.
Damage Transfer. While it is grappling a creature, the rug takes only half the damage dealt to it, and the creature grappled by the rug takes the other half.
False Appearance. While the rug remains motionless, it is indistinguishable from a normal rug.
Smother. Melee Weapon Attack: +5 to hit, reach 5 ft., one Medium or smaller creature. Hit: The creature is grappled (escape DC 13). Until this grapple ends, the target is restrained, blinded, and at risk of suffocating, and the rug can't smother another target. In addition, at the start of each of the target's turns, the target takes 10 (2d6 + 3) bludgeoning damage.
Two things about this:
(1) Grapple: the PHB states that if a player who has multiple attacks makes a grapple attack, it only takes one of their attacks. It is unclear about the "Escaping a Grapple" move. Personally I would rule that it works the same way. So if you had 2 attacks, you use one to successfully break the grapple, the other can be used as a normal attack. Others may see it differently.
(2) Damage transfer: Makes perfect sense if we're talking weapon attacks. But let's take a firebolt for example. This simplified rule ignores the fact that the rug protects the person inside it, at least somewhat. It seems unfair that 1/2 damage would transfer in some instances like this. Maybe 1/4?
I just had a party member (Monk) punch a hole through it as the killing blow and immediately don it as a poncho.