BM for Synergy was/is in development, and at one point this happened:
https://www.youtube.com/watch?v=l5Ssns5kilY
Although I’m not the one who ported it to Synergy, I was there. Also development has (kind of) stopped until they release the next update for BM. It’s playable(ish) up to the tentacles in Blast Pit, which from there on it gets progressively more broken to the point of nothing working. Currently none of the BM weapons work, most of the enemies are broken, and after the 2nd chapter most of the npcs are from HL2.