Portable Hole
Wondrous item, rare · 2014 rules, SRD 5.1
Unfolds into a 6-ft wide, 10-ft deep extradimensional hole; fold it back with contents inside. Creatures inside suffocate after 10 minutes. Mixing with a bag of holding opens an astral rift.
Also in the 2024 rules (SRD 5.2).