Will, Scion of Peace White has plenty of good lifegain cards that allow you to take advantage of Will, Scion of Peaces cost reduction ability
The deck is all about fast mana, big plays, and tons o' damage
The second ability helps fuel this
The biggest staples here are probably Elsa and Pete, leaving the other Legendary cards behind for simple slots for a Super Rare and Uncommon card that are still seeing play
Haunted Deads last ability can only be activated while its in your graveyard
Activated abilities are a huge part of the game across all colors and card types, so the question simply becomes "what can I do with two extra mana each turn?" It could be something as simple as activating Reckoner Bankbuster or an incubation token, or maybe something else entirely