Unless you have a strong art preference, it's best to save your mythic wildcards for cards that don't have a lower-rarity version
Its always three mana, and it can get through all manner of indestructible or chonky creatures
Wizards had been trying for quite some time to come up with a way of reprinting powerful staples for these tournament formats without putting them in normal sets (and therefore them being Standard-playable), and they sort of stumbled across their answer, perhaps even accidentally, in the original Commander precons
Tezzeret the Seeker I remember Tezzeret the Seeker being a much more ubiquitous card than it is now, but I dont think its ever stopped being good
Exiling a permanent and then getting a massive discount is pretty sweet
And if you can cheat Tyrranex Rex out with something cheeky, like Elvish Piper, youll be closing the game out super fast