In the default license generated by Game Maker for your games, some of YoYo Games stuff is mentioned. Are those necessary to be shipped with an application made with GM? Is it legally ok if I remove those and create my own license agreement, not mentioning Game Maker or YoYo Games in it?
tl;dr. Yes. That said:
This is not legal advice. You should seek clarification from a lawyer or from a representative of YoYo Games.
The Game Maker EULA, which you have presumably agreed to if you're using their software (unless you're using an older version to which this particular EULA does not apply, in which case you'll need to refer to it) indicates:
The Applications and all materials accompanying the Stand-alone Applications shall include a notice and End User Licence Terms:
(i) identifying the rights of YoYo Games and that they include, are based on and made using the Software;
(ii) that such end user will have no right to modify, adapt, decompile or reverse engineer the Stand-alone Applications or make any use of the Software contained therein nor to permit anyone else to do so;
(iii) that such end user must not remove, disable, modify, add to or tamper with any program code or data, copyright, trademark or other proprietary notices and legends contained within the object (compiled) code of the Software;
Both "Applications" and "Stand-Alone Applications" in this context are in reference to your games that have been produced using GameMaker. YoYo Games has provided a sample EULA, which I'm presuming is the "sample license" you're referring to, here.
What clause (i) above means is that you cannot remove references to YoYo Games or the fact that your game was created using their software. Specifically your end-user license agreement must call out all the rights that YoYo Games asserts in their EULA. You can see in the sample agreement that they do so by (among other things):
- stating the game was created using software written by YoYo Games
- asserting that the game itself is not their creation, only the software used to make it
- disclaiming liability for any damage or problems
- asserting their copyright over the aspects of the game that come directly from Game Maker
You are not required to use, word-for-word, the sample EULA. However, unless you consult a lawyer regarding modifications to the language or to the terms of the sample agreement, you could very easily violate the Game Maker EULA you agreed to, potentially opening yourself up to legal action.
Therefore I would recommend that you do not try to change the license unless you do so with the blessing of your lawyer.