I am converting an old DND mod where the BBG is a creature only described as evil ext planer creature no actual stats. it is a role playing sisyuation but With the intro into planarr and wildspace into 5e ((old gm getting ready to run my gands using 5e)) 

I know their is a banishment spell but what else might their be?

Thanks ijn advance

I am this old "Few are the heroes who are so bold, They deserve the rewards of Michlobe "

Banishment (4th level) is the most straightforward one like you mentioned, but here are some others (list may be incomplete):

Since you mention "host", dispel evil and good (5th level) can be used to end possession as well as to banish certain creatures (celestial, elemental, fey, fiend, or undead).

Similar to the above, banishing smite (5th level) can be used to banish creatures to their home plane.

Plane shift (7th level) can be used offensively, banishing a creature to a plane of the casters choosing.

Divine word (7th level) banishes celestial, elemental, fey and fiend back to their home plane.