Knife Only Achievement
Finish the campaign on any difficulty using only the Survival Knife.
The 3 knights aren’t that hard to deal with once you figure out their attack patterns, avoiding the melee attacks just requires sprinting away and with good positioning you can keep the archer from hitting you by getting behind a wall or moving to the side. In my runs I killed the knight with the sword first, then the one with the axe and finally the archer. I dont think it takes much longer than 5 minutes if done correctly.
Killing the spider only requires that you have enough heals, meaning you have to play carefully up to that point. Her melee attacks are very difficult to avoid but the other attacks can be avoided by just circling around her. The only viable strat is to tank the melee hits while circling around her to either side and stabbing it until it dies. I think it usually takes 4-7 heals depending on how lucky you get with her attacks.
The final boss is the hardest fight by far. It takes a lot of patience. you need to kill the summons one by one, while avoiding his attacks. then take half his health down and then deal with the second set of summons before finally being able to kill him. This fight might have taken me 10-15 minutes. Dealing with him by himself is easy enough, the summons are the problem, and the amount of heals you have might make a difference there.
Also, you can use the pellet gun from the shooting mini-game to shoot down the red orbs he throws since it isn’t considered a weapon for the achievement.