
Games Workshop (GW) has revealed a few details from the upcoming Tyranids Codex for Warhammer 40,000. It’s the first Codex released for 40k’s tenth edition.
The Invasion Fleet Detachment from the initially-released Tyranids Index is sticking around for the Codex, along with five new ones. No tweaks were made to Invasion Fleet, so the rules for this detachment in the Codex are the same as the ones already available in the Index.
Crusher Stampede Detachment Rule

The Crusher Stampede detachment rule makes your big beast units more dangerous the more models they lose.
Ominous Presence

Ominous Presence adds 3 to a model’s Objective Control stat, which offsets putting a lot of points into one model.
Vanguard Onslaught Detachment Rule

Any Tyranids in a Vanguard Onslaught Detachment can fall back and then charge, while Vanguard Invader units can also Charge on the same turn they Advanced.
Chameleonic

The Chameleonic Enhancement grants Stealth to a Vanguard Invader model. This means that when making ranged attacks against this model, the attacker subtracts one from the Hit roll. The model also gains Benefit of Cover, which means it adds 1 to Armour Saves.
Assassin Beasts

The Assassin Beasts Stratagem grants Precision to a Vanguard Invader Infantry unit, which means attacks can be allocated to a Character in the target unit.