My explanation for what a Vanguard format can be seen here: https://ygoprodeck.com/idk-lol/
So this is an alternative sort of deck that you could make with this sort of format (one which leans more on buffing the **** out of your vanguard unit rather than leaning heavily into extra deck shenanigans). With this one, Dark Magician is your vanguard, so you have immediate access to a lot of support spells without having to worry about losing your DM.
This hypothetical deck list of gives me an idea as of what sort of cards that would need to be either forbidden, limited or semi-limited. Namely: stat modifying cards (most likely limited due to how many exist in this game) and support cards for normal monsters like Dark Magician, Blue-Eyes White Dragon, and Red-Eyes Black Dragon.