Humanity expands into the galaxy and finds that we're alone. Just a few planets where the local primitives are figuring out how to start fires. No technological civilizations beside humanity.
We thrive, develop all kinds of incredibly powerful tech to the extent of basically "stereotypical scifi precursor species space magic" and spread everywhere before discovering some way to ascend to a higher plane of existence.

There's only one thing left to do before departing the universe, leave behind stuff to baffle whatever future civilizations develop.

Rules:
• Our resources are basically ROB-level. Shape nebulas, terraform planets, build ringworlds and dyson spheres, etc.
• The goal is trolling, not genocide. Leaving a button labeled in whatever primitive language the alien's used when we left marked "do not press this button" that when pressed fires a Halo Array = bad. Leaving one that deploys robots to find the aliens that pressed it and present them with a starfleet security redshirt certificate of genre blindness = good.

What should we build?

Temples with "magical", but never too harmful artifacts, and statues of "gods" everywhere, along with some sorts of scriptures future civilisations will be easily able to decode. These things would be relatively hidden like easter eggs, only to be found with the slightest research or be stumbled upon, and the scriptures, along with the temples and statues, would have as purpose initially confusing the new civilisations, and eventually guiding them into starting a religion which makes absolutely no sense.

With completely stupid rituals featuring stuff like, say, everyone spinning around, and singing 'trololololo' with rubber chickens on their heads as an attempt of making crops grow faster.

I know I'm not thinking too big here, but it sounds like trolling nevertheless.

Leave a large selection of clues across their originating planet via some sort of basic, space born AI that will find a primitive planet spawning and have it place objects, scrolls. Written language all that kind of stuff eluding to the secrets of the Dyson sphere.

When they finally develop the industrial tools to detect and find a massive bunker deep under their planet. Where all clues indicate this holds the plans to the dyson sphere, they open it to find that it's just a fucking, Dyson Vacuum cleaner in the shape of a ball in honor of they Dyson Sphere's creation.

Here's mine: set up a giant, flat, circular world that is held up four elephants standing on the bag of a giant space turtle. Other than this anomaly, it follows all of the rules that a normal planet also follows, and is entirely unique. Seed and uplift life on the planet, watch as they get just so confused at what screwy planet they'evolved' on. Bonus points for leaving religious texts detailing a God-like being called 'the Pratchett' that controls every aspect of their lives in subtle ways.

Here's mine: set up a giant, flat, circular world that is held up four elephants standing on the bag of a giant space turtle. Other than this anomaly, it follows all of the rules that a normal planet also follows, and is entirely unique. Seed and uplift life on the planet, watch as they get just so confused at what screwy planet they'evolved' on. Bonus points for leaving religious texts detailing a God-like being called 'the Pratchett' that controls every aspect of their lives in subtle ways.

But what if they read disk world already?

<Snipped quote by Lady Selune>

But what if they read disk world already?

They're aliens who I literally just made. Thousand monkeys with a typewriter would be the only way they could read discworld.

Leave a giant, racy statue of two of the absolute stupidest people in the history of our species carved into a mountainside for perspective future races to look upon in awe at the greatest gods of some unknown species, who were just two fucking idiots that nobody's ever gonna know they were.

Oh, and cover it in a thin layer of long-lasting stone-colored cheese for good measure.

Leave a giant, racy statue of two of the absolute stupidest people in the history of our species carved into a mountainside for perspective future races to look upon in awe at the greatest gods of some unknown species, who were just two fucking idiots that nobody's ever gonna know they were.

Oh, and cover it in a thin layer of long-lasting stone-colored cheese for good measure.

Ant and Dec?