Assalam Alaikum,
I am student and recently me and my friends have made a video game conpetetion and its free entry, and the first one to finish will get reward money. Is this legal in Islam or not

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

If the game is permissible in itself and does not include prohibitions such as nude pictures, music, and other abominable things, and it does not divert one from his religious obligations, then, in principle, it is permissible to play it.

As for the winner receiving a financial prize, then this is not permissible, because it is not permissible to take a prize on such games because the Prophet said: “Prize money is only allowed for racing camels, shooting arrows or racing horses." [At-Tirmithi, An-Nasaa'i and Abu Daawood]

The Hadeeth means that it is not permissible to take money in a contest except in the following cases: the competition on camel races, the competition on horse races, or the competition on shooting arrows and the like. The reason these three cases were made permissible is because they are skills used in Jihaad and are means of preparation and a source of strength for the Muslim nation. Some scholars included in this ruling other things that are similar in nature, as well as things that will be of benefit in general and will support Islam, such as scientific competitions.

Allah Knows best.