MTG Treachery

On resolution, the unveiling triggered ability creates a replacement effect that can apply only one time, and only until the end of the turn. This replacement effect is mentioned hereinbelow the "save effect."
Anything that triggers during the resolution of the Save effect will wait to be put on the stack until everything is put onto the battlefield and resolution is complete. The player whose turn it is will put all of their triggered abilities on the stack in any order, then each other player in turn order will do the same. (The last ability put on the stack will be the first one that resolves.)
If an effect says that the targeted player can’t lose the game, the save effect doesn’t apply.
The save effect applies any time the targeted player would lose the game, even if they’re not losing due to your life total being 0 or less. If the targeted player would have lost the game because they tried to draw from an empty library, their life total becomes 12 and they won’t lose again until they try to draw again and still can’t do so. If the targeted player would have lost the game due to having ten or more poison counters, their life total becomes 12, but they will lose the game immediately afterward because they still have ten or more poison counters.
The save effect does nothing on a player that concedes the game. A player who concedes leaves the game.
The save effect shuffles permanents owned by the targeted player into their library, regardless of who controls them.
The Save effect shuffles tokens owned by the targeted player into their library, too. The tokens they own will leave play. However, there’s no point to physically shuffle tokens into the library because the player can’t draw them as part of the Save effect and they’ll cease to exist immediately afterwards.
The Save effect doesn’t affect spells on the stack, cards that have been exiled, or permanents the targeted player controls but doesn’t own. They’ll stay where they are. Spells on the stack will then resolve as normal.
For a player’s life total to become 12, they will gain or lose the appropriate amount of life. For example, if the targeted player’s life total is -4 when this card’s unveiling ability applies, it will cause that player to gain 16 life. Alternatively, if the targeted player’s life total is 20 when it applies (perhaps because they tried to draw a card from an empty library), they will lose 8 life. Other cards that interact with life gain or life loss will interact with this effect accordingly. Notably, this means that if the targeted player can’t gain life or the life gain event is modified by another replacement effect, they might still have 0 or less life and still lose the game.

If a spell causes the targeted player to lose the game the next time state-based actions are checked (by dealing damage to them greater than their life total, for example), that spell will already be in the graveyard by the time the Save effect happens. If it’s in their graveyard, it will be shuffled into their library.
If, during a check of state-based actions, the targeted player would lose the game at the same time a creature they own would be put into their graveyard (due to an Earthquake for 10 or combat damage dealt to both the player and the creature, for example), that creature’s controller has a choice to make. The state-based actions rule is trying to simultaneously (a) shuffle that creature card into the player’s library (due to the Save replacement effect) and (b) put it into their graveyard. Only one of those things can happen. The creature’s controller chooses which one. If the creature is put into the graveyard, it isn’t shuffled into the library. Abilities that trigger when that creature is put into a graveyard will trigger only if that option is chosen.
If, during a check of state-based actions, the targeted player would lose the game for multiple reasons (for example, if they were at 1 life and had one card in their library, then Night’s Whisper caused them to draw two cards and lose 2 life), a single Save effect will replace all of them. You’ll do what the Save effect says just once.
A token’s owner is the player who created it.
If an effect states that an opponent wins the game, the Save effect doesn’t apply.
In a Two-Headed Giant game, if the targeted player’s team would lose the game during a Save effect, the team won’t lose. Instead, the targeted player will do what the Save effect says and their teammate won’t do anything. This is true even if the reason the team would lose is because the teammate tried to draw a card with an empty library or was affected by an ability that said they lost the game. The targeted player’s life total (which is the same as their team’s life total) becomes 12. The team’s life total is adjusted by the amount of life the targeted player gains or loses as a result of this, which basically means the team’s life total becomes 12.
If a card in a player’s hand has {X} in its mana cost, X is considered to be 0.
If a permanent card in a player’s hand has no mana symbols in its upper right corner (because it’s a land card, for example), its mana value is 0.

He Who Comes To Save The Day

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NOTES AND RULES INFORMATION FOR HE WHO COMES TO SAVE THE DAY