The World of Kinin
The Illithistirge is an abomination created by a druid who worships the corrupting forces of the Outer Realm. Abberation Druids revel in the bizarre, and this creation is one such manifestation.
I ran this as a standard Stirge, using the Illithid tentacles instead of a proboscis. However there are options a DM can use. Templates and similar.