This is actually really good. By gosh. There are several things I like about this.
1. You actually drew a picture to show what you have in mind. This in itself is a very formidable thing to do and definitely makes your case stronger.
2. This Orborg's highly-simplistic body design, big mouth, and crazy eyes fit the Juice Galaxy character design spectrum like a key. You deserve credit for this; it's a gift to be able to design in another artist's preferred style.
3. The proposed way to meet him. I understand Fishlicka needs to focus on concrete things first; even so, I would love for distinctive, important things to be possible to find out in the randomly-generated wilderness. With the Wawsp nest being retconned into being only one and existing near the blacksmith, this would be a great alternative to reward players who go out into the wilderness and just keep pushing it.
4. The proposed attack method. It's apparent at this point that all Juice Galaxy enemies, bosses included, have very, very simple attack code. With that, mixing up one component makes a big deal. Orborg walks like the "creator", and he summons minions from the ground like Mrs. Slitherss; each of these two alone would make a distinctive boss. Yet here you say he also swings his club.
As it stands the only character in the game who dynamically positions her/his weapon is the player. Each other character either has no separate weapon, like most common enemies; is integrated directly with it; like the Wawsp Queen and Sergeant Suckerpunch; or only has a finite number of positions to bring the weapon to, this being Mrs. Slitherss.
I don't know if you've thought of this, Gimmemilk, but depending on how this "Orborg" chooses to swing his weapon, he could be - ironically, considering he's supposed to look stupid - one of the first enemies to actually "think", by having him aim his weapon like the player can. This would be a very interesting challenge and practically open a new chapter in the Juice Galaxy gameplay book.
5. I like the detail that his right arm is longer than his left. Gameplaywise that would probably help to ensure he can hit from further away; and if the arm has joints, or is tentacle-like, then it's even more dangerous since if you get past his arm he can just pull back and club you anyway.
6. The option to take his club for ourselves is appealing. Fine-made swords and powerful guns are nice and all, but I'd like a chance to play as Captain Caveman.
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I'm not sure if you can tell, your idea here, simple as he is, has echoed some concepts and possibilities that would have me very excited in a computer game, Juice Galaxy most obviously.
I know that someone gushing is a very annoying experience, so here; let me offset my annoyance with some questions.
1. Considering what it takes to get that far out to the wilderness in the first place, does Orborg have a way of dealing with airborne players? If so, how?
2. Would Orborg's cave have any props left around that hint at why he's living in the wilderness, or if he's done anything else?
3. Gameplay-wise, would Orborg have any use for that left arm of his, or is it just decoration?