Question: what to do after you beat elite 4 sun and moon?
Answer: Catch the Ultra Beasts. A mysterious man, who turns out to be Looker of the International Police, will approach you if you leave your house after you beat the game. ... 
Get Type: Null. ... 
Capture the Legendary Pokemon & Tapus. ... 
Head to the Battle Tree. ... 
Collect All of the Z-Crystals. ... 
Get Porygon. ... 
Hatch Some Eggs. ... 
Complete Your Pokedex.