Atlas Ceiling (5e Trap)
From D&D Wiki
A massive shield of great weight is suspended from the ceiling, just before a room filled with a prohibitively deadly substance raining down from the ceiling, such as acid or fire. This shield weighs between 80 to 120 pounds, and is 15ft wide. A DC(12) Perception check can identify a small tripwire made of string made taut across the hallway that will cause the shield to fall upon whoever is below it.
When the shield falls down, any creatures below it must make a DC(15) Strength saving throw to successfully catch it, or suffer 2d10 Bludgeoning damage on a failure. If the shield is on the floor, it requires a DC(16) group Strength check by all creatures lifting it to be able to raise it off the floor and over their heads. Any creatures carrying the shield above themselves have their movement speed halved, but are able to safely traverse the dangerous room ahead.
To successfully carry the shield, the party carrying it must consist of at least one large creature, four medium creatures, eight small creatures, or sixteen tiny creatures. The shield is too small to protect creatures larger than large size and creatures smaller than tiny cannot muster enough force to lift it.
The shield confers a +3 bonus to AC to creatures under it against attacks coming from above, should the party decide that it is worth the hassle to keep it.