Single player, by 
My favorite part about this level is how unapologetically ridiculous it is. There is no storyline, as we learn at the very beginning when even a text sign tile fails to produce any text. There’s a boss at the end, but no explanation is given then either. The level exists entirely within itself, and is nothing more than a darkened, linear, sadistic romp through the emptier caves of Diamondus. It is the most basic part of JJ2 single player distilled: enemies are in your way, as are spikes, and over time you pick up food and ammo to help you. There are two moments when trigger crates became involved, but at that point I didn’t trust the level enough not to perceive them as a threat to avoid stomping until I had made sure there really was an impenetrable obstacle later on in my path.
From the very first screen, you know you’re in trouble. It’s dark, a few enemies are circulating around, and there are spikes you don’t want to fall on. A quick check reveals that ceiling spikes hurt you as well. And that’s what you need to know. There are a lot of spikes, and a lot of enemies, and they’re never really going to let up. There’s not enough ammo to use it constantly, but there’s enough so that whenever you get in a situation warranting it you shouldn’t be defenseless. Toaster and RFs won the day for me as enhanced melee weapons to take out a group of enemies quickly with more firepower than the blaster. I didn’t especially notice any moments when TNT or Electroblaster would have come in handy (outside of a trigger crate for the former), but ice had its moments against the tougher baddies, and bouncers were absent for most of the level and then presented as a lifesaving boon near the end. Seekers were, in keeping with the amount this level wants you to die horribly, nowhere to be found.
Mine of Diamondus is a good example of how to use a lot of different enemies right, in that it staggers them rather than introducing them all at the very start of the level. The more thematically specific ones, such as skeletons and ghosts, are restricted to limited areas which you may assume are more haunted than the rest of the mine. Float lizards only appear at the top of the level — which gives you the prospect of escaping the mine but in fact reveals the far background to be no more than more cave but a little farther away — and fencers and witches at the bottom near the end. (I don’t think the fencers really worked, due to their costumes, and I think they really only do appear in one spot so they would not have been missed.) The level uses two witches and incorporates them into its design philosophy perfectly in that they are presented with no show or preamble at all, are gone with as little fanfare as they appeared, and are not involved with any complicated find-Eva-type level design. Rather, you morph back almost immediately after meeting them: they’re just threats. It’s kind of amazing.
There are several secrets to break up the level, some of which are obvious and some not. The author favors layer 3 secrets that you have to shoot your way into over the ones that you don’t, so eventually I realized that it just made sense to have the blaster firing all the time, and switch to other weapons when the occasion warranted it. Secrets get bigger as the level goes on, giving you carrots and large caches of ammo instead of a measly two red gems, and were all fairly well executed. There were some I saw but never found a way into, and I wouldn’t be too surprised if they weren’t actually accessible and the level was just being sadistic, because that is so much the feeling I got from this level. It was enjoying my pain and looking for subtle, non-flashy ways to increase it. Bats would come out of the floor, secrets would not be where I expected, witches would attack without any warning at all, the top of the level didn’t offer any sight of the sky, and so on. Even the end of the level pits you against a boss in the deepest point of the cave, and there’s no suggestion that beating it will make any progress in getting you out of there, because it’s a dead end at the bottom of a long pit. Even by beating the level you are no less doomed than you were at the start. Yet determination wins out!
I’m not sure how I feel about the eyecandy… it was very basic, letting the level design speak for itself, but still I think at least a little bit more could have been done. The level was, as I’ve said, extremely linear — most of the trigger crates were even before the blocks they removed — and I don’t know whether that’s good or bad, because it certainly made the level all the more inevitable to give me no choice at any time what I would be doing next, outside of finding secrets. And there could have been more creativity in some of the obstacles. I think swinging platforms would have worked well here, and in general some enemies placed more tactfully, since at least most of them only involved getting in the right place to hit with two or three or four bullets. The important thing is to maintain the feeling that the level is deeply, deeply angry at you for something that you did — even if you have no idea what it could possibly have been and would probably apologize if the level would only provide you a text sign — and I don’t think that’s in much danger of going away. The only false note on the obstacle side was an inescapable pit of spikes near the end. Not cool.
