An easy way to clear some of the required missions is to build a working deck of around 15-17 cards and use the rest as filler for putting in spells, traps and/or ritual cards, this is so that you can use auto and still get a win and being able to use the copy deck feature so it can be easily copied to other characters.
Use cards like shard of greed to be able to get the required cards faster, or cards that can retrieve cards from the graveyard to re-use them in one duel.
Keep in mind that in the later stage, you will be required to unlock Ishizu and Odion. It is recommended to unlock them early by using a lot of trap cards and summoning a lot of Light monsters.
Do I need to win the battles for them to count?
Missions like use spell/traps # of time(s) or tribute summons and ritual summons will still count even if you don’t win the duel.
Stuck on stage 31. I haven’t unlocked weevil yet, despite having over 500 standard duelist victories, and beat him multiple times at the gate at lvl40. Any idea how I get him? Google searches aren’t telling me anything