For example, Starcraft 1 has a unit called "Hydralisk" and from what I can tell, its unique to that game. Does this mean that I can't have a unit called 'Hydralisk' in my game? I'm not going to name my game Blizzard's Hydralisk: The RTS, only having a unit bearing the same name and looks.
I guess I'm asking whether I could have a red plumber named Mario in my game too. Not whether I can name my game Super Mario: The RTS. Additionally, Lord of the Rings 'invented' the modern Orc, and it's safe to use your own Orcs in your game, I'm not clear on what the line is.
Assume that the look of the unit I want to make may be inspired by the art in that game, in that it's a slithering, mantis-bladed thing that shoots poison spikes.
This Law question suggests that names can't be copyrighted (but can be trademarked), but I'm not sure how that applies here.
US Copyright on games says:
Copyright does not protect the idea for a game, its name or title, or the method or methods for playing it. Nor does copyright protect any idea, system, method, device, or trademark material involved in developing, merchandising, or playing a game.
An example of an original creature The Beholder from DnD is featured in some games but with permission of its creators, "Beholders are one of the few classic Dungeons & Dragons monsters that Wizards of the Coast claims as Product Identity and as such was not released under its Open Game License."