I've just spent the last few hours trying to complete the boss battle with Wilhelm in Playthrough 2 of Borderlands 2. No matter what I try, I can't win this battle, and quite frankly it ticks me off so much that I now really dislike this game. I came in at level 39 and Wilhelm was 42, so I left the map and came back in at halfway through level 41, thinking it might be a closer match. However, that hasn't helped. I see loaders that spawn with skull and crossbones indicating that they are leveled above me, even though their numerical level is 39 or 40. That makes me think something's wrong.
At this point, I've respawned so many times I'm almost out of cash, and the closest I've gotten to whittling down his health is to about one-third. I've got a nice shotgun that can take care of the energizing surveyors, but they spawn a lot and don't give me a chance to battle Wilhelm much. I've tried the tactic of keeping a distance and sniping him, but that's no good because the surveyors rebuild his shield. So I've been trying to stay close and blast his critical spots at the mid-section and face, and that does take good chunks of his health with critical hits, but it's risky because of his melee spin and laser blasts, not to mention his missile launches. I'm playing as Zero, so the decoy helps, as it can give me time to run behind him and blast critical spots before it disappears.
In any case, I'm wondering how others have finished this level. It's times like this that I wonder what the developers were thinking when designing the level, or if it truly is a bug somehow, because it just seems way too difficult and takes the fun out of the game.
Best Answer
First of all, you might want to reconsider your build. My experience with Zer0 is that his builds are highly situational, and using the wrong one in certain situations can make you feel very under-powered. I used his left (sniping) tree for the majority of playthrough 1, but after getting to the second playthrough it started feeling underwhelming-- I'm now back to it, but the other builds served me better in some situations. So, consider heading to a New-U station and re-speccing. I've found that his kunai (last skill in the center tree) can be devastating against certain enemies.
Second, you might want to grab some new guns. Guns start to decay in usefulness very quickly after playthrough 1, so if you've been using the same gun for a few levels now it's probably time to replace it. Grind a bit, or spend a few of your Golden Keys in Sanctuary. The difference will astound you.
Third, take out his surveyors first, always. They are a massive pain in the butt and trying to kill Wilhelm with them healing him is an uphill battle. But leave the other bots he spawns if they're not a huge nuisance-- you can use them for second winds.
Lastly, use your elements. Shock is THE best element overall, since it has no damage penalty against any kind of enemy and in playthrough 2 deals double damage against shields. I recommend a shock sniper for Zer0-- he'll dominate with it. Apart from that, definitely bring a high DPS corrosive gun, and slag, slag, slag. Zer0's kunai can apply slag, but if you're not using that build I'd recommend getting some slag grenades-- that way, you'll be able to slag him without switching guns.