To do this glitch you have to be skilled at timing. I did this on Sandtrap.

First all you really need is 2 controls, 4 might work to. Then you have to go in forge and spawn up a gravity hammer and a missile pod.

Have one player get within picking up distance of the Hammer.

Here's the tricky part, one person has to be in the monitor (ball mode), other players normal.

You both have to grab the Hammer at the same time except the monitor pushes A on the Hammer and at the same time the other player pushes the RT.

If done successfully his arms should look weird, then the player in monitor should hold RT and push the Hammer as far as possible and the other players arms should then disappear.

There's really two glitches in one, when you have other players arms gone he can smash the Hammer and it has a long damage radius.

The other glitch is, once you have the player with a Gravity Hammer and no arms, then spawn up a missile pod and have the player with no arms walk up to it.

You have to do another timing part (when you both have to grab it at the same time except the player in monitor mode pushes A at same time other player pushes RT) and if done correctly his arms look funny.

Then the player in monitor hold right trigger and push it as far away as possible.

His arms should be gone, then player with no arms drops the missile pod and he should become invisible upon close contact and invincible. When he is far away he is visible but still invincible. Note if you swap weapons it stops.