For example, blue provides card draw with cards like Consecrated Sphinx and blue countermagic like Mana Drain or Counterspell, black offers powerful spot removal like Fatal Push and has access to the best tutors in the game in the form of Demonic Tutor or Vampiric Tutor, and white adds board wipes (Wrath of God/Day of Judgment) and recursion in cards like Second Sunrise or Faith's Reward
Baleful Strix was around $8 at the time, but the real prize was True-Name Nemesis
Jace, Wielder of Mysteries Like Laboratory Maniac, Jace, Wielder of Mysteries wins you the game if you would draw a card but your library is empty
His defining characteristic is Affinity for artifact creatures, a variant of the classic mechanic that counts your mechanical creatures to reduce his own casting cost
The larger point, and one that many players expressed in the comments below this post, was that such crossovers existing in the first place is problematic
Its almost like a toned-down Gaeas Cradle, balanced for a more modest game, but still very strong