This game straight up gets ridiculous on Mission 4. Even with saves it's insanely frustrating going in blind. Here is a youtube video
(not mine) that shows you the path to take on the maze like Mission 4.
Take note on how the vid dispatches enemies. You don't want to get on top of the boss characters before their health is low and you certainly don't want them to grab you. Honestly, you don't want to grab them either unless they are alone because their AI buddy will just charge at you the nanosecond you enter a grapple.
These boss characters are ridiculous with frame precision counter attacks (in some cases I knocked someone down, got on top of him and he recovered and attacked WHILE I was still punching on the ground!) so there is very little room for error.
Make sure you space out your save states so you don't end up trapping yourself in unwinnable situations.