This tileset is weird..
 

I was toying around with JCS, until i found two weird tilesets, qobmenu and qobduke? wonder where these came from, here are some images :
https://i.ibb.co/bKB7BKR/pukenukem.png
https://i.ibb.co/Ks42tSk/nukinwithjazz.png

Some later releases of JJ2, such as the one you're playing, included a few levels made by fans. You can check them out by opening the "HOME COOKED LEVELS" episode from the episode select menu. To see those tilesets in particular, choose "Ml_qobmenu" aka "QoB - Main Menu."

Whats with qobduke though? never seen in the main menu, hidden secret? i dunno

Levels can choose to not appear in the home-cooked levels list. This is common for single player levels that are meant to be played sequentially, so only the first can be selected there. To get to the qobduke level you are supposed to beat the other levels before it.

Qobduke is one of the extra/secret levels that came after the 'Queen of Board' level, playable by selecting Qobmenu in the Home Cooked Levels list. The level is very long, confusing, and tedious especially by todays standards so feel free to type jjnext while in game until you get to play Qobduke.