Beyond the immediate reach of the hive mind, lesser Tyranid creatures will often revert to their basic, often animalistic instincts. To represent this, at the start of the Tyranid turn any broods outside Synapse control range must take a Morale check for being All On Your Own (this being the equivalent Tyranid situation). If failed, roll for the brood's reaction on the table below.
Likewise, Tyranid creatures which fail a normal Morale check or Pinning test while beyond the range of a model with the Synapse Creature hive mind power will revert to their basic instincts. Roll on the table below to see how a Tyranid unit responds to failed Pinning tests or Morale checks when out of range of any Synapse creatures.
Tyranid Instinctive Behaviour table
| D6 | Morale Check | Pinning Test |
|---|---|---|
| 1-2 | Fall back | Pinned |
| 3-4 | Lurk | Lurk |
| 5-6 | Attack! | Attack! |
Fall back: The brood will start to fall back towards the nearest model with the Synapse Creature hive mind power. If none are on the tabletop, the brood will fall back towards the Tyranid player's closest table edge.
Pinned: The brood is pinned as per the normal rules.
Lurk: The brood will start falling back towards the nearest terrain that will give them a cover save and is not closer to the enemy. If no suitable terrain is available (ie, it's all closer to the enemy) the brood will head back to its own table edge as per the normal fall back rules.
Attack!: The brood snarls and hisses in a terrifying fashion before charging off towards their attackers! Move the unit 2D6" towards the nearest enemy unit. If it makes contact with enemy models, count this move as a sweeping advance. If the Tyranid unit is already in an assault, they count as charging in the next Assault phase.
Errata — Chapter Approved: Codex: Tyranids Q&A (v2.0): If a unit in hand-to-hand combat is forced to test for Instinctive Behaviour and rolls Lurk or Fall back, this does take it out of that combat, falling back as normal — if the opponent is no longer engaged in close combat as a result, the normal options for combat winners (pursue or consolidate) apply to them.
The full sequence for an out-of-Synapse-range Tyranid brood works as follows: (1) Test at the start of the turn to see if the unit is eligible for an 'All On Your Own' test. (2) If the test is failed, apply whatever result is rolled on the Instinctive Behaviour table. (3) The following turn, the 'All On Your Own' test is skipped — it's ignored while instinctive behaviour is already in force — but the brood's regroup test happens at the start of the Movement phase, and whatever instinctive behaviour applied continues to apply unless the brood manages to regroup. (4) A brood behaving instinctively is therefore affected twice for the same underlying cause — once when it first fails its test, and again at the start of the next turn — before it gets the chance to test to regroup at the start of that Movement phase. (5) The instinctive behaviour doesn't actually take effect until the unit moves; the regroup attempt always happens first. (6) If the unit doesn't meet all three regrouping criteria (rulebook page 73), it can't test to regroup at all, and will simply behave instinctively again the following turn. (7) If, at the start of the Movement phase, the unit is close enough to a Synapse creature, it automatically regroups instead of needing a test. (8) A unit that instinctively Attacks but fails to make contact, and is then charged in the enemy turn, is still nominally falling back — it must pass a Leadership test or be removed from play, exactly like a normal unit caught while falling back. The same applies under any other instinctive reaction, though Attack is the most extreme and most commonly confusing example.