In essence, Pact defers the cost of your spell to the next turn
If the potential winner does not respond to the DM within 72 hours, BCW will contact another potential winner, and so forth, until the prize has been awarded
There is also a practical middle ground
You can have Elspeth, Sun's Champion, Elspeth, Sun's Nemesis, and Elspeth, Knight-Errant all in play at the same time under your control because none of them shares an identical name with the other even though they all have the Legendary Planeswalker Elspeth type
Esper Sentinel definitely falls under this category as well, but we'll get to him later since he's technically not colorless
A repeatable card draw engine in mono-white, built around a strategy the color already wants to run, is genuinely hard to ignore.Why mono-white legendaries make this workThe key here is that Venat's trigger covers all legendary spells, not just creatures