This was one of the two concepts I had and an actual submission I made to Mojang, although I'm not sure if anyone like the idea. I'm finally putting it here for others to judge and see for themselves if they like it.

The Idea In-Depth: You'd have to find the Soulsand Valley to find this Skull of a once giant and mighty beast, but has been overtaken by the Nether's... "Nature". You'd then have to parkour with the jagged bones from other parts of the now dismantled body over a body of lava, and after making it across, you'd find a new storage block called "The nether Chest". This Nether Chest would be protected by a Blaze spawner, so you'd either have to quickly grab as much as you can and run, or fight them off and destroy the spawner, just make sure they don't hit you or else you fall into the depths of death.

Second (Original) Idea In-Depth: This one isn't as interesting, but it was the first one before the lava parkour one.. It's called "Skeleton Defense", and you'd find it in the same place, only instead of juimping over lava, you'd have to fight a wave-after-wave horde of wither and normal skeletons for a few times. (This play out very similar to the pillager raids, just in a big skull and not in a village). After you beat all the waves the Nether Chest would then spawn at the top of the neck bone that once used to connect to the skull but was separated centuries ago and will continue to be for centuries to come.

Please let me know which one you like better...