It is possible to gain Corpse Parts from both Casual Steel Ball Run and Competitive Steel Ball Run. You need Worthiness V to obtain any of the Stands granted from the Corpse Parts. The Ribcage and Left Arm are droppable, however the Pelvis and Heart are not.

Can you get a Pelvis from arcade YBA?

The original Pelvis can be obtained by rolling it in the Arcade. It can be sold to ShiftPlox, The Travelling Merchant (NPC) for $2,500, although this is not usually recommended as it is a very rare item. It's not droppable, meaning it can only be deleted from your inventory or sold.

What is the rarest corpse part in YBA?

The rarest corpse part is the left eye because it doesn't exist in yba B)