I unlocked the Mad Scientist and defeated him 10 times but it doesn't seem to have counted any towards the Mad Miscalculation achievement.

It also doesn't seem to be a retired achievement. Am I Missing something or is it glitched?

[Resolved - Ticket Filed & Glitch Corrected]

You may need to file a ticket about that one (don't forget about her 5-win achievement too if you don't have it). Some older challenger achievements haven't been awarding prizes since the most recent coliseum reset