10 obsidian bring ghast to the overworld

You can actually trap the ghast in the overworld so it can’t move by placing a minecart at the same level next to the portal as in the nether and making sure the 5x5 are above the block that the minecart will roll to is clear of full blocks
Screenie for overworld minecart trap (it's in the all advancements discord so you will need to join that):
/ discord