What would happen if Halaster were destroyed by adventurers?

Is Summon Greater Demon restricted to fiend?

Forge Cleric Channel Divinity option to create plate armor in 15 separate pieces. Is this a stretch or misuse of the ability?

I have a player who wants to use the Forge Cleric Channel Divinity option to create plate armor in 15 separate pieces. Is this a stretch or misuse of the ability? It feels like a violation of the spirit of the ability to me.

Spectral Defense prevents stacking with items offering resistance, thus making this much weaker than Uncanny Dodge, oversight?

PHB states new language/tool proficiency takes 250 days. Xanathar ten workweeks, errata?

Does a steed by the Find Steed ability to telepathically communicate with it’s rider require any action?