In D&D it simply compels anything with senses to go look at "something", once investigated they roll an INT saving throw per round until they realise it is bogus. Then, depending on the circumstances may investigate a wider area to find the caster or simply go back to whatever they were doing.
Might be ... Until your Illusionist Wizard get to level 14, where "something" is no longer good enough, since you get:
"Illusory Reality By 14th level, you have learned the secret of weaving shadow magic into your illusions to give them a semi-reality. When you cast an illusion spell of 1st level or higher, you can choose one inanimate, nonmagical object that is part of the illusion and make that object real. You can do this on your turn as a bonus action while the spell is ongoing. The object remains real for 1 minute. For example, you can create an illusion of a bridge over a chasm and then make it real long enough for your allies to cross.
The object can't deal damage or otherwise directly harm anyone."
Easy. Have you seen how Wish was implemented in BG2? The cast initiated a dialogue, and you chose one of the options provided. The list of options was influenced by current circumstances (for example, if a party member was dead, you could get a chance to resurrect them), and the total amount, usefulness and degree of benefit / harm the choices provide depended directly on the caster's INT. Sure, it's pretty simplistic (on the surface; the actual implementation must have been fiendishly difficult), but it's probably the best Bioware could do, considering the circumstances. I'm pretty sure many "purists" would shirk at such a limited implementation, but when ToB was released, for many people this was just "Wow!".
There are many ways to go with such things:
Simply skip the spell entirely;
Make it situational, tied to particular locations, and implemented via cutscenes. For example, we might not have the spell in the game per se, but we might have a magickal item that allows us to cast it, with limited charges. Then, as your party comes to a place for which a suitable cutscene exists and they have said item in the inventory, either one of the party members can make a remark about the item's potential usefulness here, or the item itself might start "wriggling in your backpack" (the latter was used in Dark Souls, for example).
Go the Bioware's way and implement a dialog / cutscene for every time you cast it. Development wise, this will be the most challenging one.
I'm pretty sure Larian would have their own ideas, if / when they ever come to implement something as heavily dependent on player's imagination as your example.
Originally Posted by RagnarokCzD
Problem here is that you are comparing game wich have rules set for few hundert of years and nobody even know for sure theese days why wich figure plays the way it plays ...
