From Regular Rare to Ultra Rare and Special Art Rare, there are many different gradations that make collecting and playing exciting
Easily milling two cards a turn is a nice boost, stocking your graveyard with potential reanimation targets at no cost
This means there are decks that can make Odins instant kill a recurring threat and one that the opponent will need to burn resources to neutralize
Spark Double also seems key, since Gyruda, Doom of Depths triggers whenever it enters the battlefield if you can mill a reanimate a Spark Double you can make a non-lgendary copy of Gyruda, Doom of Depths, giving you another enters the battlefield trigger to repeat the process
If you want him for a deck, wait for the asks to fall in line with the sales, because right now the trend is working in the buyers favor
Sorry for the random order