FabFilter

Has anyone figured out a way to get Pro-MB to do OTT-Style multiband upwards limiting? My attempts have resulted in weird hyper aggressive mangled sounds but I feel like it should be possible (yes, I know Xfer OTT is free, just doing this out of curiosity).

Its very hard to match the same style and sound as OTT with Pro-MB. At minimum, you need 2 instances of Pro-MB, one to mimic the downward compression, the other to mimic the upward compression. But even then, I've tinkered with Pro-MB settings this way and have a hard time making it as hard-nosed and present sounding as OTT. Here's a ZIP with my Pro-MB OTT downward and upward presets, which use the same crossover and roughly similar settings to OTT, which you could use as a starting point to tweak further:
drive.google.com/file/d/1Pyv5QiZIEgXxUsJEW-wyz1G2gCCzVlEy/view?usp=sharing

One tricky aspect is that when you dial in OTT on a sound, you really want to change the threshold for both downward and upward compression for a band at the same time, and when using Pro-MB you are forced to change those thresholds across 2 different instances of the plugin.