While this card is on your field, you can't lose the game, and opponents can't win.
When your leader's defense becomes 0 or less, bury this card and change your leader's defense to 1.
QThis amulet is on my field and my leader's defense is 2. My opponent has 2 copies of Dracomancer's Rites on their field. It's now the start of their end phase, and they've discarded a card this turn. Do I lose the game? In other words, would the relevant abilities be resolved in the following order?
1. My opponent deals 2 damage to my leader with one Dracomancer's Rites.
2. This amulet's ability is triggered, so I put it into its owner's cemetery and change my leader's defense to 1.
3. My opponent deals 2 damage to my leader with the other Dracomancer's Rites.
ANo. At the start of your opponent's end phase, the abilities of both copies of Dracomancer's Rites are triggered and become pending. Your opponent starts by resolving one instance of the ability, dealing 2 damage to your leader. Since your leader now has 0 defense, this amulet's ability triggers and becomes pending.
At this point, there are two pending abilities: the other instance of Dracomancer's Rites's ability for your opponent and this amulet's ability for you. When both players control pending abilities, the active player resolves theirs first. Therefore, your opponent must resolve the remaining Dracomancer's Rites ability, dealing 2 damage to your leader and bringing its defense to -2.
Lastly, you resolve this amulet's ability, putting it into its owner's cemetery and changing your leader's defense to 1.
QIf an enemy Deepwood Anomaly deals attack damage to my leader during my opponent's turn while this amulet is on my field, bringing my leader's defense to 0 or less, does my opponent win the game?
ANo. When the enemy Deepwood Anomaly deals attack damage to your leader, its ability triggers, and at the same time this amulet's ability triggers, since your leader's defense has become 0 or less.
When both players control pending abilities, the active player resolves theirs first. In this case, your opponent is the active player, so they resolve Deepwood Anomaly's ability.
At this point, this amulet is still on your field, so its effect "you can't lose the game, and opponents can't win" is applied at the same time as Deepwood Anomaly's effect "win the game," which is nullified because prohibiting effects always take precedence. As a result, your opponent doesn't win, and their Deepwood Anomaly's ability becomes resolved.
Then, you resolve this amulet's ability, putting it into its owner's cemetery and changing your leader's defense to 1.
QCan I concede while this amulet is on my field?
AYes. All players may concede at any time, regardless of card abilities.
QIf I lose due to tournament rules (running out of time, etc.) but I have this amulet on my field, do I still lose the game?
AYes. Card abilities have no influence over tournament rules.
QIf an enemy Deepwood Anomaly attacks my leader while this amulet is on my field, do I lose the game?
ANo. If a card's effect instructs a player to perform an action ("win the game") that is prohibited by another active effect ("you can't lose the game, and opponents can't win"), the prohibiting effect takes precedence.
QIf my leader's defense changes from 0 to 1 with this amulet's ability, does Elana's Prayer's ability trigger?
AYes, it does.
QIf I have 2 copies of this amulet on my field when my leader's defense becomes 0 or less, can I put only 1 copy into its owner's cemetery?
ANo. You put both copies into their owner's cemetery and change your leader's defense to 1.
QIf I draw a card when my deck is empty, but this amulet is on my field, do I lose the game?
ANo, you don't.