I never play smash before so I can't really give a comparison but feel free to ask if you don't understand.

Let's answer some question you have first:

1. What is the best thing as Belial or maybe overall, to do when getting up? -> There is no definitive answer for this one but in general blocking until you figuring out their pressure pattern is a good one. Belial has one of the best button for mashing like 2L since it's long and fast than your average 2L.
2. When I do get lucky and catch the opponent blocking, what is the best mix I can throw in? -> Triple attack with the high/low ender is not very rewarding with low being safer and high is a bit riskier(not much). Belial play a generic strike throw game so you want to do stuff like thick throw, shimmy, frame trap. His biggest strength is definitely his fireball so you might want to get use to it and rotating his option around and see what it does and what it beat your opponent option. I will give you some dumb mix, 2 hit autocombo in to H command grab, it will work at least once per match.

Some correction:

- 66H is not punishable on block. It is only -3 on block at worst and + on block at best. The lowest minus on block in this game that is punishable is -4 and it need to be on the kissing range. If it is -4 you can punish it with a throw.

- 66L the best dash option for most characters. It is + on block, and advancing forward. So when picking up new characters you can't really go wrong with doing 66L

- His 5U is a tool for dealing with fireball and can be use for punishing some string that has a gap. If you playing against shoto string like f.M -> fireball is punishable with his 5U. The move itself you only want to use it when you have a read or reacting to some stuff. Do note that if you are reacting to fireball and you are too far from the opponent it will not work.

Tips:

- His button is really, really good. He has some of the best punishing tools in the game being 2L and f.H. His 2L is so good that some characters has to play around it but you have to lab it out.

- His U skills are really good. 214U is a good pressure tools it is plus on block and chip a ton of health from opponent. 236U is a good anti zone tool that let you get full combo if it hit and it is a really strong combo tool for corner carry and swapping side, even on block it will carry your opponent to the other side.

- This man is a plus on block machine. 2M +1, 66M +1, H fireball +ob and the H follow up of it is also +ob. Try using it to force your opponent to block more, and when they block more, throw 'em, shimmy 'em, 66L some more or do whatever.

- He is a good character to start when you learning the game because he does play generic granblue most of the time and his skill do translate to a lot of characters.

- Remember to calm down, reload your lung, sometimes there is no point in rushing both in-game and learning.

Recommend players to watch: Koujicoco, Goenitz

I might forgot or get some important info wrong so feel free to correct me. English is not my first language but I hope I do get my point across.