The comitative is rare and not used in spoken Finnish. It expresses the presence of something. It often corresponds with "in company of" or "together with".
|tyttö koirineen||the girl and her dog(s)|
|mies perheineen||the man and his family|
|pienine perheineni||with my small family|
|papereineen kaikkineen||with all the papers|
|tohtori Virtanen puolisoineen||doctor Virtanen with his partner|
|Hän tuli kauniine vaimoineen.||He came with his beautiful wife.|
The comitative ending is -ne, and always in the plural. A singular form doesn't exist, but plural forms are always used, no matter if the meaning is singular or plural. The nouns require a possessive suffix as well. The comitative is formed using the strong-grade plural stem (the same stem you use for the (mihin).
|Minä menin saunaan ystävineni.||I went to the sauna with my friend(s).|
|Sinä menit saunaan ystävinesi.||You went to the sauna with your friend(s).|
|Hän meni saunaan ystävineen.||He went to the sauna with his friend(s).|
|Me menimme saunaan ystävinemme.||We went to the sauna with our friend(s).|
|Te menitte saunaan ystävinenne.||You went to the sauna with your friend(s).|
|He menivät saunaan ystävineen.||They went to the sauna with their friend(s).|
Notice that the verb doesn't get plural when you include other people in the sentence!