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Great topic, I like it!
You named Katamari Damacy, and that surely is one really silly game (while also having unique and great gameplay). I genuinely smiled about all the stuff I could roll up and the reaction. The panic my Katamari induced and how all living things kept fidgeting stuck to the Katamari. Or police man shooting at the Katamari (not that it helped them in any way).
Other great funny games are some of LucasArts adventures. Especially The Secret of Monkey Island And Day of the Tentacle have absolutely great jokes. The Sword fighting in Monkey Island, which you win with the best insults and retorts. Also word plays jokes like with the Monkey wrench. And Day of the Tentacle where you travel through time with the chrono John (yeah, a toilet) to prevent the toxic spill that mutates an intelligent tentacle to get arms and take over the world:
https://www.youtube.com/watch?v=2BRXmgcBHBM&ab_channel=GeneralBeef
Ron Gilbert worked on these games, especially Monkey Island. He later on in times than LucasArts was no longer made another funny game, The Cave. About a talking Cave narrating the game and the people search for their desire inside it.
To move on to another game: the Lego games generally tend to be very lighthearted and fun. The most interesting for me personally is Lego City Undercover, which clones Open World Sandbox games like GTA and makes fun of their conventions and tropes. And let me tell you: if you think Lego games are for kids, then I pose the question why the intro has a visual reference to Boogie Nights (the rollerblade girl), a movie entirely *not* for kids. It is because adults can have very much fun with these games as well!
Not a classical light-hearted game, but I think Duke Nukem 3D is quite funny at times, with joking references and comments. The end boss of the first chapter you fight on a big footall field, while cheerleaders are cheering throughout the fight for instance.
And one of the silliest games I ever played has to be Worms. It took the gameplay of Scorched Earth, but added a lighthearted component by introducing worms as characters and add absolutely silly weapons and unwanted destruction. If you ever played Worms with friends together in hotseat at one computer, you know it is one of the most fun experiences, as your turns do not always go as planned.
Also quite funny is Battle Chess. The idea was simple yet enticing: it is normal chess, but if you capture a chess piece an animation plays that shows them fighting. This has a lot of gags (and also blood).
