This is a sister editorial to my other one on monsters and the importance of sanity checks with them. The two were effectively written in parallel. In the first, I was notably critical of going too far with design, hailing the necessity of sanity checks to keep the design from going crazy. Here I'm going to go slightly in the other direction, acknowledging a few of the current problems with monster design.
Folks often claim they like and want unique monsters. And, in part, they aren't lying. They also aren't telling the truth. It's the squeaky wheel syndrome. Initially the primary requirements are pretty consistently fulfilled, so the complaints tend to go more towards secondary or tertiary concerns. I'd like to introduce something that most folks don't consider: While there may be technically infinite unique monster designs out there, there's a far smaller subset that fulfills the requirements of fitting into the game neatly and providing monsters that feel 'enemy' instead of 'mutant sludge from planet reject'. Limiting to the second, you get maybe a few hundred thousand possible designs. Maybe a million or two, but you're probably highballing it there. This limitation is really mostly irrelevent of the game. Some things, no matter whether they fit the game's theme or not, just don't make good monsters. The range of what falls within the millions that work is amazingly broad and diverse, ranging from everything from carebears to Cthluhu. One could easily believe that such a broad set includes everything. I assert that not only is this false, but when combined with the goal of fitting the game neatly, it rules out more than it includes by far. In other words, the goal of creating creatures never before seen is at odds with the goal of creating monsters that belong in the setting and theme.
What does this really mean though? Originality shouldn't be the highest god of monster design. Orcs have their place. So do ogres. Are they the limit? Of course not, but trying to go for the ultra-unique sludge with toes sticking out of it isn't the solution to making the monsters more interesting. Monsters, when well used, can provide a lot more than some art drawing, name, and set of moves. Let's take a look at Earthbound. The enemies, in many cases, added to the setting. They were wacky. They were goofy. They blended with the theme. They did this without abandoning the notion of seeming dangerous. The emphasis was not on creating the most unique monsters, though they certainly got a few of those in there, but on creating monsters that felt appropriate to the theme of the game.
By considering the environment and working your monsters into it instead of working on monsters in a void, the artists get a better sense of a creature's logical parameters, and can produce far more effective designs that contribute to the overall atmosphere and experience. These monsters may or may not be unique, but they definitely belong and by belonging add to the sense of reality that the game world possesses.