diff --git a/crates/engine/tests/integration/main.rs b/crates/engine/tests/integration/main.rs
index fac0eefaf6..8c6a9da811 100644
--- a/crates/engine/tests/integration/main.rs
+++ b/crates/engine/tests/integration/main.rs
@@ -767,6 +767,7 @@ mod repro_pilot_crew;
 mod rhys_evermore_remove_counters;
 mod riot_control_regression;
 mod ripples_of_undeath_regression;
+mod riptide_gearhulk_5994;
 mod rite_of_consumption_damage;
 mod roots_of_wisdom_if_you_cant_draw;
 mod roughshod_mentor_green_trample_grant;
diff --git a/crates/engine/tests/integration/riptide_gearhulk_5994.rs b/crates/engine/tests/integration/riptide_gearhulk_5994.rs
new file mode 100644
index 0000000000..6c77fa06a0
--- /dev/null
+++ b/crates/engine/tests/integration/riptide_gearhulk_5994.rs
@@ -0,0 +1,116 @@
+//! Runtime regression for issue #5994: Riptide Gearhulk's per-opponent ETB target
+//! fanout must be OPTIONAL ("up to one target"), so declining a target for an
+//! opponent does not fizzle the ability.
+//!
+//! Riptide's ETB — "When this creature enters, for each opponent, put up to one
+//! target nonland permanent that player controls into its owner's library third
+//! from the top." — lowers to a per-opponent fanout with
+//! `MultiTargetSpec { min: 0, max: PlayerCount { Opponent } }`. Before the parser
+//! fix, the "put ..." verb fell through `per_opponent_target_fanout_min`'s
+//! "gain control of"-only anchor and each per-opponent target lowered as MANDATORY
+//! (`min: 1`); declining one then made the ability fizzle (and the harness's
+//! required-slot check panics), which is what these tests would catch on a revert.
+//!
+//! https://github.com/phase-rs/phase/issues/5994
+
+use engine::game::scenario::{GameScenario, P0, P1};
+use engine::types::game_state::WaitingFor;
+use engine::types::identifiers::ObjectId;
+use engine::types::mana::{ManaType, ManaUnit};
+use engine::types::phase::Phase;
+use engine::types::zones::Zone;
+use engine::types::PlayerId;
+
+/// Riptide Gearhulk's verbatim Oracle text (keywords carried separately).
+const RIPTIDE_ORACLE: &str = "Double strike\nProwess\nWhen this creature enters, for each opponent, put up to one target nonland permanent that player controls into its owner's library third from the top.";
+
+const P2: PlayerId = PlayerId(2);
+
+/// {1}{W}{W}{U}{U} funded into the pool so the cast auto-pays and never surfaces
+/// a `ManaPayment` window.
+fn riptide_mana() -> Vec<ManaUnit> {
+    vec![
+        ManaUnit::new(ManaType::Colorless, ObjectId(0), false, vec![]),
+        ManaUnit::new(ManaType::White, ObjectId(0), false, vec![]),
+        ManaUnit::new(ManaType::White, ObjectId(0), false, vec![]),
+        ManaUnit::new(ManaType::Blue, ObjectId(0), false, vec![]),
+        ManaUnit::new(ManaType::Blue, ObjectId(0), false, vec![]),
+    ]
+}
+
+/// CR 601.2c (issue #5994): declining EVERY per-opponent target must resolve the
+/// ability, not fizzle. In a three-player game (two opponents) with a nonland
+/// permanent under each opponent, casting Riptide and declining both optional
+/// per-opponent targets leaves both permanents on the battlefield and resolves
+/// cleanly. If the `min` lowering reverted to 1, the per-opponent object slot
+/// would be REQUIRED and the harness could not decline it (a required-slot panic).
+#[test]
+fn riptide_declining_all_per_opponent_targets_does_not_fizzle() {
+    let mut scenario = GameScenario::new_n_player(3, 42);
+    scenario.at_phase(Phase::PreCombatMain);
+    scenario.with_mana_pool(P0, riptide_mana());
+
+    let p1_perm = scenario.add_creature(P1, "Opp1 Bear", 2, 2).id();
+    let p2_perm = scenario.add_creature(P2, "Opp2 Bear", 2, 2).id();
+    let riptide = scenario
+        .add_creature_to_hand_from_oracle(P0, "Riptide Gearhulk", 4, 4, RIPTIDE_ORACLE)
+        .id();
+
+    let mut runner = scenario.build();
+
+    // Declare no object targets: every optional per-opponent object slot is
+    // declined. (Player intent is offered so player slots, if any, are satisfied.)
+    let outcome = runner.cast(riptide).target_players(&[P1, P2]).resolve();
+
+    // CR 601.2c: the ability must actually RESOLVE (return priority), not stall
+    // mid-resolution. This is the discriminating check: a mandatory (`min: 1`)
+    // lowering does not produce declinable per-opponent target slots — it halts at
+    // a non-targeted `EffectZoneChoice` and never reaches this Priority window, so
+    // the assertion fails on a revert.
+    assert!(
+        matches!(outcome.final_waiting_for(), WaitingFor::Priority { .. }),
+        "declining every per-opponent target must resolve the ETB back to priority, \
+         got {:?}",
+        outcome.final_waiting_for()
+    );
+    outcome.assert_zone(&[riptide], Zone::Battlefield);
+    outcome.assert_zone(&[p1_perm], Zone::Battlefield);
+    outcome.assert_zone(&[p2_perm], Zone::Battlefield);
+}
+
+/// CR 601.2c (issue #5994): with two opponents, the controller may choose a target
+/// for ONE opponent while DECLINING the (optional) per-opponent target for the
+/// other, and the ability still resolves — moving only the chosen permanent. This
+/// is the discriminating "one selected, one declined" scenario: a mandatory
+/// (`min: 1`) lowering would force a target for the second opponent too.
+#[test]
+fn riptide_selects_one_opponent_target_and_declines_the_other() {
+    let mut scenario = GameScenario::new_n_player(3, 42);
+    scenario.at_phase(Phase::PreCombatMain);
+    scenario.with_mana_pool(P0, riptide_mana());
+    // Give P1 a library card so the moved permanent's "third from the top"
+    // placement has somewhere to sit; P2's permanent is untouched anyway.
+    scenario.add_card_to_library_top(P1, "P1 Library Card");
+
+    let p1_perm = scenario.add_creature(P1, "Opp1 Bear", 2, 2).id();
+    let p2_perm = scenario.add_creature(P2, "Opp2 Bear", 2, 2).id();
+    let riptide = scenario
+        .add_creature_to_hand_from_oracle(P0, "Riptide Gearhulk", 4, 4, RIPTIDE_ORACLE)
+        .id();
+
+    let mut runner = scenario.build();
+
+    // Choose P1's permanent for P1's slot; declare no target for P2 → P2's
+    // optional per-opponent slot is declined.
+    let outcome = runner
+        .cast(riptide)
+        .target_players(&[P1, P2])
+        .target_objects(&[p1_perm])
+        .resolve();
+
+    outcome.assert_zone(&[riptide], Zone::Battlefield);
+    // The chosen permanent left the battlefield for its owner's library.
+    outcome.assert_zone(&[p1_perm], Zone::Library);
+    // The declined opponent's permanent is untouched.
+    outcome.assert_zone(&[p2_perm], Zone::Battlefield);
+}