Immovable rod

An immovable rod is a magical iron rod that becomes fixed in space when activated. While active, it can ignore most of the effects of gravity.

Description
An immovable rod can be activated by pressing the button on the end, at which point the rod becomes stationary and nearly impossible to move. It is not subject to normal gravity, and can support up to 8000 pounds, although it will deactivate and fall normally if more weight is placed upon it. The DC to move an immovable rod is 30, and even on a success it will only move 10 feet at a time.

Campaign One: Vox Machina
Vox Machina had several immovable rods at various points that they used with some frequency.

The party acquired the rod at some point prior to their adventure in Kraghammer, and Tiberius Stormwind used it as an anchor so he could drop a captured Fomorian from a height into K'Varn's lair. However, he did not retrieve the rod. Some time later, Jordana Whisk gave Keyleth another one in Whitestone.

Vex'ahlia used the new rod, again as an anchor, to get through the sand trap in the Cavern of Axiom. Pike used the rod and some rope in a similar way to help the party cross a river in the Feywild. Scanlan used it during the fight against Umbrasyl, to attempt to pin the dragon into place by activating the rod within Umbrasyl's stomach, while Umbrasyl was in flight. The dragon was able to move, but the rod caused him injury. Vex'ahlia then retrieved it.

Vox Machina found another rod in Emon following their defeat of Thordak, and used the pair of rods to hold back several boulders as they prepared to fight Raishan. Grog used the rod to help push in one of the Prime Trammels as the party banished Vecna, and then to prevent himself from falling as Entropis began to collapse.

Campaign Three: Bells Hells
In, Laudna uses her Immovable Rod to keep a crate blocking a shade creeper hole.

During the Twilight Mirror Museum heist, Laudna twice jammed the doors right before the Verdict's grasp. One time in the foyer, then, using the same rod, did this trick with the door between marionette's room and the door with Xhorhasian artifact.

Trivia

 * The Dunamancy spell Immovable Object allows the caster to grant the object on which it is cast properties very similar to those of an Immovable Rod.