Kind of like getting a player head, except you can install their limbs. Not sure if this is possible, but would be pretty funny to have someone else's arm.

Could be done and would be a fun aesthetic upgrade. I'll try to implement it at some point.

Can Mobs get critical hits on players? I was thinking that if they can (and they have a weapon like a sword or axe) that they have a chance to chop off an arm or leg on crit. It would probably need to be disabled by default, but it could be a interesting addition for brutal hardcore type of play. I'd suggest making a peg leg craftable for players as well but making it have a speed reduction. Maybe with it able to be crudely put in place with a right click in exchanged for some health, and and even larger speed reduction, since your player probably isn't as skilled at doing so than the robosurgeon.

If one player manages to chop off all of another player's limbs without killing them.

Achievement: "Alright, we'll call it a draw."