MTG: creature and enchantment triggered to opposite effects

Question

The situation is my Mortus Strider has been enchanted with Unholy Indenture.

The creature has

when it dies, return it to his owner’s hand

The enchantment says

When enchanted creature dies, return that card to the battlefield under your control with a +1/+1 counter on it.

Who gets the creature? Me or my rival?

Does the creature ability trigger before or after enchantment?

Answer 1

Assuming you control both the Mortus Strider and the Unholy Indenture, you get to choose which ability will resolve first. If your opponent controls the Unholy Indenture, it depends on whose turn it is.

The position of spells and abilities on the stack decide the order in which they resolve. Players can only cast one spell at a time, so their order is never in question. However, multiple abilities can trigger at the same time. When that happens, there are rules how to determine their position on the stack:

603.3b If multiple abilities have triggered since the last time a player received priority, each player, in APNAP order, puts triggered abilities they control on the stack in any order they choose. [..]

"APNAP" means "active player, non-active player". The "active" player is the one whose turn it is. If multiple players make a choice at the same time, the active player makes the first choice, followed by all others in turn order.

Therefore, assuming you control both the Mortus Strider and the Unholy Indenture, you get to choose the order of these abilities on the stack. You put the ability you want to resolve first on top of the stack.

If you control only one of those two and your opponent controls the other, then the order depends on whose turn it is. If it's your turn, you put the ability of the object you control on the stack first, and your opponent's ability second. Therefore, your opponent's ability will resolve first. If it's your opponent's turn, the opposite happens.

Answer 2

The answer is: It depends who's turn it was and who controlled what. For the purposes of this I assume different players control the aura and the creature (the question implies that but is not explicit) We'll say Player A controls the creature and Player B controls the aura.

These are triggered abilities, both triggering at the same time from the same event. When that happens these triggers are put onto the stack in AP/NAP(Active player/non-active player) order according to the Comprehensive Rules:

603.3b If multiple abilities have triggered since the last time a player received priority, each player, in APNAP order, puts triggered abilities they control on the stack in any order they choose. (See rule 101.4.) Then the game once again checks for and resolves state-based actions until none are performed, then abilities that triggered during this process go on the stack. This process repeats until no new state-based actions are performed and no abilities trigger. Then the appropriate player gets priority.

Spells and abilities on the stack resolve in reverse order to how they were put on the stack. That gives two possibilities:

• If it is Player A's turn or a player before Player A but after Player B in multiplayer

  1. Player A's Mortus Strider's ability goes on the stack first as they are the first player in AP/NAP order.
  2. Player B's Unholy Indenture's ability goes on the stack second.
  3. The stack starts to resolve, hitting Player B's Unholy Indenture first. This returns Mortus Stider to the battlefield under Player B's control with a +1/+1 counter.
  4. Player A's Mortus Stider's ability is reached on the stack and tries to resolve, but the connected card is not found in the graveyard and thus can't be moved from that zone, so it fails.

• If it is Player B's turn or a player before Player B but after Player A in multiplayer

  1. Player B's Unholy Indenture's ability goes on the stack first as they are the first player in AP/NAP order.
  2. Player A's Mortus Strider's ability goes on the stack second.
  3. The stack starts to resolve, hitting Player A's Mortus Stider first. This returns Mortus Stider to Player A's hand.
  4. Player B's Unholy Indenture's ability is reached on the stack and tries to resolve, but the connected card is not found in the graveyard and thus can't be moved from that zone, so it fails.

If both the aura and the creature were controlled by the same player, it would be that player's choice which order their triggers are put on the stack, likely the Strider first and the Indenture second, so the last one put on the stack would resolve and all other triggers would fail.