This is called duplicate protection and is the topic of today's guide
It seems to be serving double duty for Wizards, as a unique collectors item for judges, and a way to build up more The Brothers' War hype
With energy and these other high-powered cases, you have a mechanic which blurs those lines and smooths out a lot of the potential variance between draws
For example, if a 5/5 creature that's also a planeswalker with three loyalty counters on it is dealt 4 damage, it's been dealt 1 excess damage and Aegar's ability may trigger
It is a Planeswalker that can consistently draw cards on every turn
A 2/4 flier for three mana is great, and on top of that, it can facilitate a lot of lifegain in your angel or cleric tribal decks