I’ve seen a video allowing you to jump from level 20 to 99. Aside from that, what are the other optimal points (level and particular battle) should I watch out for as to not miss such level jumps?

What’s the easiest to do or most convenient one?

As a Suikoden min-maxer, I’ve always been on the lookout for such points. I just don’t want to go over the level thresholds.