Placing a bag of holding inside an extradimensional space created by a Handy Haversack, Portable Hole, or similar item instantly destroys both items and opens a gate to the Astral Plane. The gate originates where the one item was placed inside the other. Any creature within 10 feet of the gate is sucked through it to a random Location on the Astral Plane. The gate then closes. The gate is one-way only and can't be reopened.
-DMG pg. 153
It was fun for one boss fight, but is being retired after the rule of cool.
Placing a bag of holding inside an extradimensional space created by a Handy Haversack, Portable Hole, or similar item instantly destroys both items and causes a magical explosion. Any creature within 10 feet of the explosion must succeed on a DC 15 Constitution saving throw or take 6d6 force damage and is pushed 10 feet away the source. On a successful save, the creature takes half as much damage and isn’t pushed. In addition, unsecured objects that are completely within the area of effect are automatically pushed 10 feet away.
Damage may or may not stay at that. We'll see.
