The plan is for planeswalkers to be mythic rare by default, but if a design team feels that a rare (or uncommon) planeswalker would serve the set, they have access to it
In reanimation shells, resolving this early usually means drawing 7 to 14 cards immediately and assembling whatever black spells in MTG you need to close the game
Your opponents will need to find a way to out this card, or it will be much harder for them to challenge you throughout the match
Now, some Modern decks can win the game before most decks can even cast Jace, so it was only fair that this planeswalker was unbanned
Part of that is that people are building a lot and the game is popular, and part of is that EDHREC spent the last year trying to get the daily scraping routine to finish faster, resulting in data days and sometimes weeks earlier than before
Fortunately, this is exactly what Doctor Doom, King of Latveria does, making Green Goblin a premium upgrade