Hello, the following points may be helpful:
1-Video games have been becoming popular in the world, so their bad effects are unavoidable.
The above sentence is logically wrong. Popularity does not necessarily bring about bad effects which can not be avoided.
-in the world= all around the world.
2-The purpose of my presentation is that to introduce you to the disadvantages of them.
-that should be removed from the sentence.
3-Violent video games should be banned, in my point of view, I fully agree with this topic.
-From my point of view = in my opinion
-You havenít introduced any topics. You could simply say:
Iím strongly for (agree with) the idea of banning violent video games.
4-Letís begin by the effects on aggressive behavior, psychology and cognition.
-letís begin with.
-The sentence implies that video games have some effects on the behavior of a person who is already aggressive. So the games trigger/provoke aggressive behavior.
-Psychology: study of mind, perception, cognition, and so on. So you mean ďpsycheĒ.
5-they still include.
6-Fighting scenes are applauded that players may watch and bring violent actions to the real life
-I donít seem to understand your point here. Maybe you mean:
Some (psychologists) are concerned that violent scenes to which players are exposed may encourage violent action in real life.
7-For example, recent researches conducted on video games show that 89% of such games contain some violent content.
8-Repetitive Strain Injure/ injury.