Like most Magic: The Gathering cards, the value of Finale of Devastation depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Commander Masters)
Some cards received lowball offers, while others received at least 90% of their fair market value
There are plenty of unknowns about TCGL that will be revealed in the future, but you may wish to go to sources outside of KoopaTV to hear about those
The token created by Nissa's first ability has its power and toughness set only once, at the time the ability resolves
It's mediocre at best, but might be alright in human/soldier tribal if you have enough historics to trigger it a lot
While you control it, cards that are "decorated" (which the card uses to refer to cards with "premium" foil, alternate art or frames, and promo cards) have a miracle cost of one snow mana (which means that you can play the card for one snow mana if it's the first card you drew that turn)