Nobody knows how Mindlorgs look. Because they can control things, confuse players. For example: You find some precious ore. But when you mine it, you realise that it's only stone. You see a stag running around. But it's a bear or etc.. You are mining. But it's hard to control the mouse. You don't need to buy a new mouse, it's a Mindlorg! Illusions disappear when you kill the Mindlorg. I don't think they could attack you. They would try to confuse you by teleporting, disguising as other mobs or etc.. It would be cool of having a special helmet which would block all confusions. As I mentioned before, Mindlorgs don't have a look. They are always disguising as monsters or npcs? They should be really rare , even on specific planets. Let me know what you think about Mindlorgs.
Sounds interesting, but could you give us more information about the Mindlorgs. What do they look like in their true form? (if they have one, or are they always posing as different enemies?) What kind of items would they drop? I was thinking about what you said about the special helmet that could block confusions, what if that was one of the drops of a Mindlorg so you still have to fight one to obtain one? You said they are always disguising as monsters or npcs but do they live in a specific biome which has those monsters and npcs, or are they everywhere? I think you're off to a good start but it needs a little more information.
What about if they are rare but when captured they are confused and start morphing into a randome assortment of species changing every second. As far as their discovery maybe they go into their true form (previously named gelatin creature) when attacked. They should also disguise themselves as a peaceful creature. Finally do they attack directly or just cause problems? P.S. Feel free to pick and choose any of these ideas or take none at all. It is your creation afterall.
It's a great idea, the only point i don't like is this: It would be damn frustrating and wouldn't add fun or fun-kind-of-difficulty to the situation.