I'm not exaggerating either, as it would go for about $30-40 with the next most expensive card generally being Mox Opal at $20
Theres not much more to it than that, in terms of rules
For this added cost, you get a ton more value, as Sephiroth can easily draw you a card upon entry
Other diabolical interactions include Dark Wings Bring Your Downfall plus Breath of Fury, I Am Never Alone in a Kiki-Jiki, Mirror Breaker deck, My Crushing Masterstroke plus sacrifice outlets, and Approach My Molten Realm with either my boy Heartless Hidetsugu or Malignus
The Pikachu Illustrator card is widely regarded as the rarest and most valuable Pokmon card ever created
Oh, and you get to exile it, so your opponent can't get up to any shenanigans with that card themselves