Levelengine's SMW hacks contain enough shout outs to warrant their own page. Most of these are through level names. Other references to outside media and the like are also listed here.
In Stellar View, to get the secret exit, you must carry a key across one of the areas with a Phanto-like sprite that's chasing you, which looks like J-Dog.
Nightfall. "Nightfall was a take at replacing SMW Central that went on air for a brief period in January, 2008. Needless to say, it didn't actually hit the amount of expectations originally intended for it and SMW Central eventually returned from its grave." Bits of the image as seen in this thread were redrawn in YY-CHR and cobbled together to create the visuals for this 2-part level.
Fort Nidhogg. References the video game Nidhogg, also throwing in what looks like Mario doing his victory walk into the mouth of the Nidhogg as he clears the 2nd part of the 2-part level.
The Myth of Ratatoskr, which fittingly has Mario climbing up and down the inside of a giant tree if Norse mythology is anything to go by.
Ferocious Beasts was the name of a level in another Mario romhack, specifically Super Compact World which Levelengine livestreamed on his channel.
May the ballroom remain eternal has the "rolled up newspaper" painting by Ivan Seal in its background, mainly recognizable for being the cover art of the first album in The Caretaker's Everywhere at the End of Time series.
Jettison III. Again, the title of a 6 part song off the Buckethead album Coat of Charms, sharing its name with the final levels of Levelengine's other two romhacks that were built during the 12 days of Christmas.
The Colossus Killer (Colossus 2)
None of these names are final as this is still a work in progress, but currently include Into the Twilight Forest, Acai Berries, Perpetual Burn, Irritating Stick, AST, and Death Over Other Means.
had the same name)