Java Edition:Adult Zombified Piglin Chicken Jockey
Normally, only baby zombies and zombie piglins are supposed to be able to spawn as chicken jockies. However, some bugs existed which would allow an adult to become a jockey. Before 1.21 Pre-Release 1, stacked mobs could not enter portals, so these mobs can only be in the Overworld until then.[1] Zombification in the End also became possible later, but only after this bug was fixed.
Obtaining
Zombification
From 20w07a to 20w11a, due to a bug[2], when a piglin zombifies in the Overworld it can rarely turn into this mob. The chance of this happening is usually 0.25%, but this may be increased to 0.4875% by having a non-mounted chicken within a 5x3x5 area centered on the pigman.
Piglin Jockey
Using the Piglin Jockey method in 20w21a, an adult piglin can be obtained on a chicken. If this piglin on a chicken is zombified in 1.16.2 Pre-release 1 or later it will become an adult zombified piglin chicken jockey.
22w13oneBlockAtATime Mob Wrestling
In the April Fools' version 22w13oneBlockAtATime, the player can pick up nearly any entity to create mob stacks in any combination. This powerful method also allows for the Adult Zombified Piglin Chicken Jockey to be obtained.