Bring back the undead monsters such as gibdos, redeads, redead knights, cull the bokofos/lizalfos/mobfos amounts give us the Stalfos Knights back give us some spooky ass ruins with floor masters and wall masters some Rats n Ropes and definately give us the Poes could you imagine walking through Thyphlo Ruins and seeing unlit lanterns on the ground only to have them ignite with ghostly flame and start kicking the crap outta link? Darknuts and IronKnuckles would've worked ridiculously well in BOTW as would've soldiers from games like ALTTP, have it as corrupted armor by the power of goopyboi and boom yer set to go. Give us Aquatic monster not nearly enough of those.
One thing i really hated though, silly as it seems, we really didn't get many opponents that were overscaled for link, we had Molduga, Hinox and the Blights but that was really it, when bar the likes of Morpha most bosses in the series have in general been massively overscaled to links size (TP bosses for instance) i think with such a massive world open to us we could've had big ole world bosses and i mean BIG like Morpheel levels of size.