Java Edition:Skeleton Spider Jockey in The Nether/End
Until 1.21 Pre-Release 1, stacked mobs could not go through end or nether portals due to a bug.[1] This along with the fact that spiders don't spawn in these dimension means that, normally, the player couldn't obtain a skeleton jockey in either of these dimensions. Using spider spawn eggs. However, the player can force spiders to spawn in these dimensions. Spawn eggs can only be obtained in 11w49a by going into creative, which means some people consider this cheating. Alternatively, this jockey can be obtained in the April Fools' version 22w13oneBlockAtATime.
Obtaining
Spiders can be spawned by directly using the spider spawn egg or by creating a spawner using the egg from 14w28b (1.8 snapshot) or later.
End
1% of spiders will be the spider jockeys. If the player wants to use the spawner method they must obtain the spawner item because there are no spawners that naturally generate in the end.
Nether
In versions 12w36a (1.4 snapshot) and later 80% of skeletons in the nether will become wither skeletons creating a wither skeleton spider jockey. Before 12w36a, 1% of spiders would be the normal skeleton jockey. After 12w36a, 0.8% of spiders in the nether will be wither skeleton spider jockeys and 0.2% of spiders will be normal skeleton jockeys. For the spawner method, the player can either place a spawner item or find a naturally generated blaze or magma cube (20w16a (1.16 snapshot) and later) spawner.
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 skeleton spider jockey in the end or nether to be obtained.
Recontinued
In 1.21 Pre-Release 1, the longstanding bug MC-67 was finally fixed. In this version and later, spider jockeys can be sent through portals recontinuing skeleton spider jockeys in the nether and end.