A boundary attack makes the arena edge part of the threat rule. A left rune marks Kern's entry from 0.55 seconds and fixes one horizontal lane. Tavi clears it before the 1.72–2.28 second crossing, then approaches only after Kern strikes the opposite wall. The cue, camera, collision, and opening all refer to the same boundary event.
At 0.55 s the left boundary rune expands and previews one fixed horizontal corridor. Tavi begins moving upward while Kern remains staged outside the playable rectangle; the warning identifies side, direction, width, and release timing.
Autoplay is disabled by reduced motion. Scrub across 0.55, 1.72, 2.28, 3.15, 3.75, 4.55, and 5.35 seconds to inspect the boundary contract.
Implement the boundary source, entry cue, committed lane, active crossing, exit state, camera support, and return route as one explicit sequence whose collision matches its visible geometry.
Pair the boundary with a directional cue that remains readable before the attacker enters: a rune, shadow, dust wake, portal, silhouette, sound pan, or camera lead. The cue must identify the exact edge and distinguish a crossing lane from an arena-wide effect. In the example, the left rune starts 1.17 seconds before collision.
Keep warning and collision in separate states. The dashed corridor is information only; the solid lane is active from 1.72–2.28 seconds and uses the same stored centerline and width. End collision when Kern hits the opposite wall, not when the effect fades, so the promised opening begins on an observable event.
The player needs enough view and time to locate the origin, understand direction, and move a full collision shape clear. Clamp or lead the camera so the cue cannot sit behind UI or outside the frame. For multiplayer and split views, replicate one committed source and provide equivalent world-space signals to every participant.
An off-screen attacker that becomes visible only after contact tests memory or luck rather than spatial reading. Move the signal inward, extend the warning, pan the camera, or reserve the attack for a boundary the player can currently inspect.
A vague screen flash can make the whole perimeter feel unsafe and erase useful positioning. Mark one source, one direction, and one footprint; if several edges can activate, preview their order and leave a reachable response route.
An attack may originate beyond a physical wall, outside the navigation mesh, or merely outside the current camera. Store the world-space source first, then derive presentation for each camera; otherwise camera motion can silently move the perceived attack origin.
Validate the lane against walls, platforms, summons, and player spawn points before commitment. Do not let another system place an unavoidable hazard in the only exit during the warning, and decide whether the source can be intercepted before it enters.
An attacker that leaves the playable area needs explicit targetability, collision, cooldown, and return rules. The example ends danger at wall impact, permits one sword hit, then shows Kern taking a non-damaging outer route back to the source.
Inspect narrow phones, ultrawide displays, camera shake, zoom, local co-op, subtitles, and HUD-safe areas. Verify the first warning frame, the last escapable frame, the first active frame, the exit, interruption, death, and loop seam.
Kern charges a rune beyond the left wall, breaks through the marked corridor, and lodges in the opposite seal. The same architecture explains the entry signal, the fixed lane, the impact opening, and the outer path used to reset.
Tavi uses ordinary movement to leave the announced corridor, not invulnerability or an off-screen guess. After collision ends, the short approach to the lodged boss makes the sword relevant without turning the warning itself into an attack opportunity.
A wide swing or beam may begin from a visible boss inside the arena. A boundary attack is defined by a source outside normal playable space and by the information needed to project that source inward. Forced scrolling moves the frame or arena continuously; teleport relocates without traversing the announced lane.
Kuro repeatedly enters the burning route from beyond its playable lane. Her silhouette, flight direction, and environmental cover make the edge of the screen an authored attack origin while forward route progress remains visible.
Shriek leaves the arena and returns in horizontal passes. Dark motion at the screen edge and the prior background fly-by communicate which boundary will become the source, separating directional warning from the damaging foreground crossing.
During Maelstrom, Leviathan becomes unavailable while a large portal outside the platform marks the origin of a straight dive-bomb. The portal translates an off-arena 3D source into a camera-readable direction that can be combined with hazards already on the floor.
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