I want to make a cartoon video describing my personal experience. Is it okay if I used the past tense to introduce the story first and then shift to the present tense to make it sound more realistic? I have seen comedians doing this, but I am not sure whether they were making a mistake or it was actually acceptable to do so.
The most natural tense to use when talking about the past is past tense so it is perfectly right to use it when giving introductory and background information about yourself. I base this assertion on material in the Creative Non-Fiction module during the first year of my Masters in Creative Writing
After that, there are several benefits to writing the script for your video about the past in the present tense. Principle among these are that you can share a lived experience with your audience in that you are talking about emotions, events and people from the past as if you are experiencing them anew. This can give a freshness to words that would not otherwise be present if you were talking about events as if they were dead, dusty and departed.
There are, of course, several pitfalls to avoid when speaking of the past in the present tense. Some of these are: it can feel unnatural to talk about the past as if it is happening now (so try not to let this show too much); listeners can have a hard time following the tense shift (so try to counteract this by making it clear when these events occurred); and reliving sensitive events as if they were happening now can be disturbing to the narrator (so try to keep it light). This being a comedy video, you shouldn't really have a problem with the last point.
In conclusion: it is said that 'remembering happens in the present tense' and so you should be fine shifting to the present tense to make your video sound more realistic.
Good luck with the project.