FoC manipulation and "new" deployment options are based on the various stages and methods of a Tyranid invasion. The design goal is to be able to represent in a viable manner things like stealthy vanguard forces, huge waves of little gribblies, the sheer brute force of monstrous creatures in the final stages of invasions, surprise forces coming from underground and the sky, and so on. Pretty exciting to know that someone in charge acknowledges that Tyranids are multi-faceted.
Further details that the others did not mention:
- A lot of flexibility in the form of army composition. As opposed to the very mutable stats of units and weapons of the old codex, which caused a lot of headaches for opponents.
- Hive Tyrants are the main source of FOC manipulation. The idea is that they can specialize the scoring elements of the army.... but you have to pay for it.
- Reserve manipulation is a very strong theme in the codex. These options are more numerous and reliable than in the current codex. And that's because...
- Mycetic Spores have expanded rules for ease of use. This includes MC broods.
- Trygon tunnels are also greatly expanded. Raveners have additional synergy with the tunnels. Even Monstrous Creatures can use them but with a penalty.
- More outflanking options. Various ideas are being thrown around on the topic of protecting Genestealers and especially Lictors from being shot to pieces when they appear.
And the most important rule that is being tested...
Synapse offering protection from Instant Death in a brand new way. Right now this is being tested only on creatures that have the Synapse rule (not within the aura): Wounds that trigger ID can instead be rolled to either cause 1 Wound, 2 Wounds, or ID. The designers have mentioned that multi wound models are problematic in the ruleset and doubly for for Tyranids who have many such units, yet because of the abundance of S8 and above weapons they cannot rely on them
