Here's a module I just finished up a module for both a CR 30+ encounter with a deity (druid moon god) within the beast lands. This module also includes a cr 13 encounter with this deity's avatar in Iriaebor.
The avatar fight is suppose to give nothing as the body and all of its stuff disappears when the avatar's hitpoints reach zero. The Moonlit Grove fight can give the potential of granting the party random magical items, 200,000 gp. If the party has a druid grant that druid access to two custom spells level 9 "Forecrest's Moonray" and level 8 "Mortal Bane", as well as depending on what deity that druid worships a custom artifact "Nature's Beginning and End." Mind you the Forecrest god form is based off a level 30 druid so the npc sheet is pretty big with all the possible actions and spells. The Avatar is much more manageable as it's restricted power to a level 13 druid.
Yes both have spell taking sells from both cleric and druid lists it's a big complicated to explain why (because this is based off my old character from a campaign), i'll just say that he has access to the cleric spell list for reasons. As a result i gave him the spell list based more around the healing aspect, making the god encounter if it turns into a battle a war of attrition. If you chose to play the npc that way anyways.
EDIT: It is a mod for 5e
EDIT 2: I've changed the attached mod as to avoid any copyright problems. The tokens for the God and Avatar have been changed to the box standard "G" and "A" tokens.
EDIT 3: will bring the mod back when i have a new map for the encounter
EDIT 4: The person i was going to have make a map for me, got swamped so i am just putting up the basic without map version of the module, and update when i have a chance to make it myself, or he gets freed up.
Attachment 30362
Final Update: I finally have made my own map for it (sorry for the low quality, this was my first try at map making.)
Attachment 31919