Vortex Monolith

A monolith rewrites the sky. This one paints the screen with the effects that hang around the Vortex Pillar during the lunar event, and that is the whole function: no enemies, no music change, nothing spawns. Toggle it by hand or wire it to a switch or timer like any other mechanism. It can also go in a vanity accessory slot, where the effect follows you around the world instead of sitting in one room.

A placed monolith applies while it is on or near your screen, so the area it covers scales with your resolution rather than being a fixed square of tiles. Walk far enough away and the effect fades out.

The lunar monoliths do not combine with each other, so lining up all four gets you one of them rather than a blend. They do combine with the Blood Moon and Aether ones, and there the order you flip the switches changes the result: a lunar effect turned on first and then the Blood Moon gives a different tint than doing it the other way round. When several are running, the game scans from the top left corner and the last one it finds wins, which means the lowest and rightmost monolith takes over.

The lunar effects raise the apparent light level, and on the surface at night they brighten the whole screen. Parked in a social slot, one of these is effectively free night vision for exploring or building after dark, which is more use than a pillar souvenir has any right to be.

The four pillar monoliths and the Void Monolith are crafted at the Ancient Manipulator, so they are all lunar event leftovers. The others come from everywhere else: the Blood Moon Monolith drops from Dreadnautilus while fishing a Blood Moon, the Radio Thing comes off Deerclops, the Aether Monolith is what you get for shimmering an Angel Statue, the Cyborg sells the CRT and Retro screens, and the film projector comes from dropping a platinum coin into an oasis pool.

Two of them behave oddly. The Radio Thing applies The Constant's sepia filter, and inside The Constant itself it does the reverse and switches the filter off. The Aether Monolith has three positions rather than two: off actively suppresses the aether visuals even where nearby shimmer would normally produce them, low leaves things exactly as they were, and high forces the effect on.

The Void Monolith copies the Moon Lord fight's screen effects and takes its name from the slabs in the Space Odyssey books. The Party Center is a monolith internally, but it is the one that starts a real event instead of just painting the background. And if you leave one running when you quit, the background lingers for a moment on the way out, the same fade you get when switching it off by hand.