2006 "Gold Star" Holo Shiny Charizard: $25,405 Finding that limited gold star on a Pokmon card makes it worthwhile, but discovering a shiny Pokmon is like hitting a jackpot on the slot machine
As a flying, lifelink 3/5, it rewards gaining and losing life by handing out +1/+1 counters or reanimating creatures from your graveyard
Source (includes a link to the exhibition page with full details)
This alone makes it a powerful card, but if you activate the second ability on Academy Ruins, on your upkeep to put Mindslaver back on the top of your library, then you draw it on your turn, repeat the process, and play the game alone
Being able to sacrifice the big creature you Stationed it with to get a massive hand refill is very, very efficient for just three effective mana and two life