Is Tribal a permanent type (for Muldrotha)?
Tribal is a card type but not a permanent type.  So Tribal counts for cards like Tarmogoyf, but not Muldrotha, the Gravetide.

From the comprehensive rules:


  110.4. There are five permanent types: artifact, creature, enchantment, land, and planeswalker.
  
  300.1. The card types are artifact, conspiracy, creature, enchantment, instant, land, phenomenon, plane, planeswalker, scheme, sorcery, tribal, and vanguard.