Hi there,
Ignore got nerfed so that is nearly useless these days (see updated REG for changes). While ignored characters still cannot enter battle the ones who are already in battle are now treated differently so that the battle ends in a stalemate if nothing else happens (according to my understanding).
So if "ignore" is one of your main reasons to go for multiple brigades this is no longer a danger IMO. Benefit of multibrigade characters (beginning of dual brigades) is that you can play more great stuff off of them. E.g. while playing mainly black defense one or two black/gray guys with low numbers would allow for playing the new Unsuccessful too (to just give one example).
In offense with the meekifying of heroes you often automatically get to 2 brigades if you use these guys. But also other great heroes like Jeshu, Restorer; Joshua, Conqueror, Music Leader etc. bring you multibrigade flavour in your deck.
Very often offenses + defenses are still build around one of those brigades mainly. For more details I recommend all the great videos out there from Jayden, Tyler, Hymn, RobM and others which take closer looks on deck building and related topics.
Since multibrigade is all over the place today cards like Treacherous Land and similar are also very beneficial.
