Is the intent of the Shadow Sorcerer to be able to cast Darkness by expending any spell slot?

Pegasus from Greater Find Steed then True Polymorph it into a Silver Dragon Wyrmling…

Grimgates, Arlathan and Spellhold same location, or nah?

Who are the Hethcanters?

Opportunity attacks can only be made when a creature leaves an enemy’s reach with the exception of Polearm Master, correct?