What happens when two continuous effects in the same layer have the same timestamp?

When two continuous effects exist in the same layer and neither is dependent on the other, their timestamps are compared to determine application order. If the timestamps are truly identical — which can happen when two effects are generated at the same time — the game uses a tiebreaker: the active player's effects apply before the non-active player's effects (APNAP order), and if both are controlled by the same player, that player chooses the order (CR 616.1).

Dependency is checked first (CR 613.7–613.8). One effect is dependent on another if applying it first would change whether, what, or how the second effect applies. If dependency exists, the dependent effect applies after the one it depends on, regardless of timestamps.

If neither effect is dependent and they share a timestamp, CR 616.1 states that simultaneous effects are applied in APNAP (Active Player, Non-Active Player) order, with the active player's effects applied first, then the non-active player's, then within each player's group the player chooses order.

Example: Suppose both players' spells resolve at the same time (e.g., during a multi-spell situation) creating two type-changing effects on the same permanent in Layer 4, with identical timestamps and no dependency. The active player's effect applies first, then the non-active player's, meaning the non-active player's effect ends up on top — typically making the non-active player's effect the 'last applied' and thus decisive for the final result.

In practice, true timestamp ties are rare because effects usually get timestamps when they're created, and simultaneous creation is handled by APNAP ordering. The key takeaway: check dependency first (CR 613.7), then use timestamps (CR 613.6), then APNAP (CR 616.1) to break ties.