How to get higher lvl soldiers and bosses/Heroes? ?

[Will Drowned]

hi so yeah how do i get better soldiers because im playing as sheikah cadre and i can only get aghnim soldiers the ones that throw needles and artillery , how do i get other kind of troops cuz i dont think i could be able to win only using ahgnim infantry, also how do i get bosses or heroes ? cuz ive seen videos were theres a bongo bongo among sheikahs and a wierd twili dragon what do i have to do to get them ? i checked wikia but it doesnt say how to get them or summon them thanks in advance.

[Saria's Vanguard]

You need to upgrade your castles and the next blacksmith and barracks will unlock, for heroes, they appear after certain events or time passed. There is also the probability that some are in custom battles but not implemented in the campaign yet for one reason or another