My first rules foray into 5e; I'm going to be running a campaign at the library in March, and wanted to dip my toe in. Since Pantheist Clerics are a thing I've been writing about for 20 years or so, this seemed a good place to start, and aligned with a conversation folks were having on the Playground.
Some priests do not choose a particular deity to worship, and instead embrace the full pantheon of their people. Unlike more specialized priests, these clerics can perform ceremonies for the entire pantheon; they may pray to Kelemvor at a funeral, invoke Lathander upon a birth, bless soldiers in the name of Tempus, and open a harvest festival in the name of Chauntea (or Waukeen, or Llirra, or all three).
Being a Pantheist cleric can be a difficult balancing act, especially for an adventurer. Depending upon their alignment and personality, a pantheist cleric will undoubtedly have certain deities whose philosophies they favor, and others whom they are less sympathetic to. However, pantheist clerics serve an important role in the worship of many deities; while it may be somewhat illegal to worship deities such as Mask, Chemosh, or Iuz, a pantheist cleric can invoke them as needed, often serving as a link between worshipers and their deity in out of the way places, or serving an isolated community's varied religious needs.