So, if a caster, say a Warlock 17 Hexblade Pact of the Blade uses True Polymorph on himself. He needs to concentrate but if he concentrates until the full hour is up, it lasts until dispelled? In his new form, the warlock can only talk and cast spells if his new form allows such actions. Does this mean that if he is turned into a creature with it's own innate spells that he can cast those only? or does he still know his own spells (with the charisma of the new form). If he becomes a creature that could talk and potentially cast such as say a Drow instead of human that he could still use his class abilities including spells in the new form? I can see all kinds of complications here. and the spell doesn't affect shapechangers so does that mean that he couldn't use True Polymorph to become say a grey slaad?