Once you unlock and play through more gates, you obtain completion bonuses such as Gems, structure decks for an archetype, cards, and elemental orbs
You might have noticed that this card has a lot in common with Sun Titan
(Note that the card was not originally a Shapeshifter in creature type because, at the time, legendary creatures were creature type Legend.) The challenge to the design was to create a mono-black creature that felt like a Shapeshifter
You'll lose the ability to quest immediately with him, but the trade-off is being able to play an eight-Willpower Bodyguard (that heals itself) on turn four instead of turn five
Its definitely too low-impact for much Commander viability, but its a sideboard staple when its in Standard since its difficult for blue decks to handle
They're not actually on the battlefield, so they're not entering it or leaving it