This pack replaces a few mobs with Stranger Things Monsters!
They even have custom animations (most of them are idle ones – you have to look closely!) Replaced mobs:

• Evoker – Vecna
• Warden – Demogorgon
• Mind Flayer – Ghast
• Demodog – Spider

Note that this pack is experimental and may contain bugs!

Requires either OptiFine or ETF and EMF to work!

Screenshots: !Vecna !The Demogorgon !The Mind Flayer !The Demodog