The Warhammer 40k 10th edition battle-shock rules are very simple. You take a Battle-shock test for a unit by rolling 2D6 and attempting to equal or exceed its Leadership stat. If the test fails, you can’t target the unit with Stratagems, it can’t contest objectives, and you risks losing models when it falls back from combat.
That last rule is called a Desperate Escape test. During our demo game of Warhammer 40k 10th edition at Warhammer Fest 2023 we learnt that this means rolling a D6 for each model in the unit falling back, and removing one as a casualty for each roll of a one or two.
You’ll make a Battle-shock test in your Command phase for each unit you control that’s below half strength. For units with multiple models, that’s when half or more of the models are dead; for units of a single model, you test when it’s got less than half its starting wounds remaining.
That’s a big difference: it means that vehicles and monsters are both now susceptible to Battle-shock and the effects of morale.
The hideous Warhammer 40k factions are chock full of nasty things that can force enemy units to take Battle-shock test at other pointsin the game. Chaos Knights project an aura of palpable dread, the Death Guard Plagueburst Mortar forces a Battle-shock test on any enemy unit it hits, and the Tyranids can force a Battle-shock test on the whole enemy army once per game using The Shadow in the Warp.
This is a big change in how 40k represents morale. In 9th edition 40k failing a leadership test causes models to flee from the unit, effectively doing a little extra damage to the squad. The new rules impair a unit’s ability to perform its role in the army, both controlling objectives and using Stratagems, representing how faltering morale erodes the effectiveness of a fighting force.