On my last playthrough (it was a multiplayer one) me and my friend were grinding the post-plantera dungeon for the wepons, when within like, 5 seconds of each other we got a tactical shotgun, a shadow beam staff, and a sniper rifle.
On that same world, in the first two jungle chests we found, there were a bezor in each.
When Moon Lord grinding, we got 5 rainbow crystal staffs.
On a different world, I got two pieces of aichent shadow armor 1 after another.
Pirate invasion, pillars, and blood moon (or was it solar eclipse, I can't remember) all at the same time.