when I send mobs in the end fountain specifically the shulker it ends up at spawn, except it's 32767 blocks in the air. I found this out when I wanted to make a shulker farm in the overworld so I did testing in creative. I sent the shulker through the end fountain and when I went through and I saw it for a split second and then it wasn't there so I did /tp @s @e[type=shulker] and it was at spawn, but really high in the air. Shulkers don't fall and I would have to load the chunks even if they did so the only way I could think to get it down was to send a boat in after the shulker fly up with fireworks load the chunks get in the boat and when you're about to hit the ground you place water, but this is very tedious and all my shulkers just died so...