Soulguard

"Soulguard" (ソウルガード Sourugādo) is a Keyword that allows monsters to avoid leaving the field (destruction, returning to hand, ect.) at the cost of discarding a card from the soul of that monster.

It is marked by the text: 

Ancient World

 * Duel Sieger "Spartand"
 * Gold Dragon, Abend
 * Martial Arts Dragon Emperor, Duel Sieger
 * Space Dragon Emperor, Galiazond

Danger World

 * Armorknight Archangel
 * Armorknight Cerberus
 * Armorknight Iblis
 * Armorknight Succubus
 * Dense Forest Dragon, Radica
 * Fighting Dragon Emperor, Demongodol Ark
 * Fighting Dragon, Demongodol
 * Steel-blooded Dragon, Gavaldine
 * Super Combidragon, Brainbaltes

Dragon World

 * Crimson Battler, Drum Bunker Dragon
 * Dragon Knight, Geronimo
 * Dragon Knight, Spartax
 * Drum Bunker Dragon, "Dual Wield"
 * Drum Bunker Dragon
 * Drum Bunker Dragon Father
 * First Crimson Chieftain, Greatest General
 * Iron Fortress Dragon
 * Jackknife "Aggressor"
 * Jackknife "Beistand"
 * Jackknife "Burn Energy"
 * Jackknife "Dispersal"
 * Jackknife "Jaeger"
 * Jackknife "Savior"
 * Jackknife "Thunder Storm"
 * Million Rapier Dragon
 * Skyblue Dragon, Crystal Saber
 * Super Armordragon, Aura Sword Dragon
 * Super Armordragon, Buster Cannon Dragon
 * Super Armordragon, Drum Breaker Dragon
 * Super Armordragon, General Boldness
 * Systemic Dagger "Onca"
 * Systemic Sword Dragon
 * Thunder Knights, Drum Bunker Dragon
 * Ultimate Sword Dragon
 * Zweihander Dragon

Dungeon World

 * Brave, Drum
 * Brave of the Sun, Gao
 * Demon Lord, Joker Grunwald
 * Guardian Dragon of Demon Lord Castle, Deukruzar
 * Guardian Dragon of the Ruins, Meteor Rain
 * Legendary Warrior, Gao
 * Master Skeleton
 * Tosa Hound, Cobalt

Generic

 * King the Dominator

Hero World

 * Infinite Robo, Mathematics
 * Rescue Dragon, Force Arms

Katana World

 * Sky Rush, Garyu-oh
 * White Dragon Hermit, Nanase

Legend World

 * Armored Dragon, Cuelebre
 * Valkyrie, Brilliant Brynhildr

Magic World

 * Great Duke, Astaroth
 * Super Tough! Asmodai

Star Dragon World

 * Demon Blaze, Maxwell

List of Cards that give Soulguard

 * Arts of Heat Haze
 * Dragonic Trust
 * Ultimate Buddy!

List of Anti-Soulguard Cards

 * Ninja Arts, Half-kill

Rulings

 * If a card is destroyed, but it is prevented from leaving the field with Soulguard, cards or abilities that activate when that card is destroyed (such as Penetrate) will still be activated.
 * Cards with Soulguard may be used to pay for call costs or card effects that require cards on the field to be sent to the drop zone, such as the call cost of Fighting Dragon, Demongodol, or the cast cost of Castling. In this case, the cost is considered paid even if Soulguard prevents the card from being sent to the drop zone.(Source)