There are a number of creatures I'd likely never have used in my own adventures that I've gotten the chance to use in pre-published modules I've run -- the old Age of Worms adventure path was my first time running a grick, and probably the first time I ever actually used a shrieker the way it was designed to be used. Low-level fourth edition LFR adventures included lots of needle blights, which didn't excite me at all as a DM.
But the creature I currently can't see ever facing or putting into an encounter, which actually exists in the fifth edition Monster Manual, is the awakened shrub (p.317): a CR 0 creature that can only be created via a spell which requires a minimum 9th-level spellcaster to spend 1000 gold pieces on a material component which is consumed on casting.
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Pauper
But the creature I currently can't see ever facing or putting into an encounter, which actually exists in the fifth edition Monster Manual, is the awakened shrub (p.317): a CR 0 creature that can only be created via a spell which requires a minimum 9th-level spellcaster to spend 1000 gold pieces on a material component which is consumed on casting.
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Pauper