I recently discovered what specifically was making A Koopa's Revenge 2 incompatible with the Ruffle emulator. I'll save you the technical details, but the beta version of the game now works pretty much perfectly in Ruffle. The next update to the game will work in Ruffle and will default to Ruffle automatically on Newgrounds. Until that's ready, here is the beta/demo that works in Ruffle:

https://www.newgrounds.com/projects/games/528371/preview/filetype/0/emulate/flash

Unfortunately Ruffle lacks copy/paste functionality as of the time of writing, so you can't import your save without typing in the code one character at a time. To get around this I hard coded a special password to give you 107% completion. Just type "giveme107" into the import save file field and click import save to give yourself full completion.

Ruffle compatibility has inspired me to get a working version out sooner. The update has been suffering major scope creep, and thus has been delayed for literal years. So what I'm going to do is instead of waiting until version 3.0 is 100% ready, I'll be releasing a v2.9 some time soon, probably in the next month or two. The rest of the planned/promised features and assets for 3.0 are still coming, just at a later date.

Also, Boss Rush is done now. It requires a completed save game to access. It still needs some polish, but it's 98% done. See if you can overcome the challenge.

That's enough rambling for now. Smell ya later.