For a Dog deck, this gives you an easy way to expand your canine army beyond its usual limited cardpool, leveraging token generators like Gleeful Demolition to swarm the board with vigilant 3/1s
Use an old Energy or Common Pokmon card that you have extra copies of
Lastly, the Registry allows me to send my collection to card shops and bulk graders, so they can help me find the elusive cards I still need to complete my sets, like that Fighting Energy in a 9.5 from 1st Edition Gym Heroes, which only eight people sent in to grade, and I need to complete my set
Avacyn, Angel of Hope Speaking of big threats, one of the biggest, most powerful angels in all of Magic is Avacyn, Angel of Hope
A card can only be in one zone at a time, and which zone its in currently changes how the rules refer to it and how you can use it