MAME version 0.245 was just released, officially supporting the game now. No more need for unofficial pre-release builds of MAME.

And one thing stood out in particular in the change notes:

• 9827: marblmd2.cpp: Removed divide-by-two on clock, running the CPU at 14 MHz like Batman, and hooked up EEPROM. [David Haywood]

That's basically a double CPU speed overclock for the game. That's gonna have a big impact on eliminating the slowdown that I see in all the playthroughs.

Hi Dwedit! Thanks for letting us know about the official MAME support!

We were aware that the initial custom build had some slowdown, which you can see in some of the earliest runs. A revised custom build came out a week later that corrected the CPU speed, which you can see in more recent runs (including all of the current podium times at the very least).

I just installed the new MAME version and can confirm that the game plays exactly like the 2nd custom build that we have been playing on for a bit now.

Hooray for official support! Hopefully more runners will come!

Thanks, didn't know about the second custom build that fixed the clock speed.