thick card sleeves Beckett Shield Rigid Holders Protects cards when handling or storing Platinum Protectors Thick Penny Sleeves

(And yes, multicolor creatures count for purposes of this question.) White Giant White Merfolk White Treefolk Blue Elemental Black Elf Black Goblin Black Faerie Green Kithkin White Treefolk, Black Faeries and Green Kithkin

If you manage this, you'll earn a very cute Pikachu-themed emblem

Planning ahead can give you some great combinations

The most likely reasons are if it's sacrificed, if it's legendary and another legendary permanent with the same name is controlled by the same player, if it's a planeswalker and another planeswalker with the same subtype is controlled by the same player, if it's a creature with toughness 0 or less, or if it's an Aura that's either unattached or attached to something illegal