Hey guys, first time poster here. I found a few new tricks recently that I don't think anyone else has found yet.

First, by using the sentinel, you can skip the boss cutscene and kill GR666 in approximately 30 seconds:

Second, on level 15 (arcade mode, also works in the campaign mode), you can shoot through the wall and jump out of bounds, falling to the end of the level:

Cheers,

BronchoPanza