|Don't sweat missing these on your first playthrough, they become MUCH easier on later runs when you are a higher level (because you retain your level/weapons). None of the bosses in the early parts of the game have achievements associated with them. Each boss after Kaine gets unfrozen has an achievement associated with it. |
Obviously, you are going to want to attempt these achievements on the "easy" difficulty. Learn the boss patterns and make sure you skip all cut-scenes (using ) associated with boss intro/death scenes. I won't really go into Boss strategy because you honestly don't even have to try to get most of these. Each of these achievements should pop after a boss cut-scene ends. If you are worried about missing them, make sure you use the mailbox before each boss to save, and simply load your game if you missed the target.
The last 'time-limit' boss achievement will only be obtainable while going for Ending C or D, and it is a little tougher than the others to obtain due to the massive amount of projectiles. Dodge your way around them and use your weapon to cut through them when you are close. Once you are able to hit her, spam your attack and with a little luck the achievement should pop.