The most valuable cards from the Base set typically include holographic rare cards, first edition prints, and cards featuring popular Pokemon
In short, to be considering Radagast, you need to be a very diverse, creature-heavy deck
That single card accounts for roughly half the opening value in a lucky box and it sits alongside Arceus V SA (112/100) at 8,980 (~$64) and a Hyper Ball UR that trades at more than almost any trainer item card in the Sword & Shield era
At maximum, his ultimate ability will quickly end the game once it goes off, though it is arguably a tad win-more
This attack does 40 damage for each of your Pokmon in play that has the Round attack
Not every player will get their copies of Harsh Mentor right away, so I think this guy could follow the same type of price model as cards like Stony Silence or Rest in Peace