I have collected all the rumors I could find and am going to post them all in one go for you to read and dissect, there is a lot so ensure you have plenty of time to read, there are also some links to Bell of Lost Souls, our most reliable rumor mill. Enjoy and apologies if any rumors are repeated.
4 New Tyranid species never before seen in a codex, one of which will make the current carnifex "look like a dwarf". ~I assume this would be the plastic Trygon and the Mawloc
Tyranid Characters return... No so much individual creatures like Old One Eye, but these will be indicitive of big creatures that have survived through battlefields and evolved into something better.
Plastic Hive Tyrant kit with wings.
Codex is in the can and is written by Robin Cruddace (of codex Imperial Guard).
Tyranids will have evolved rules and abilities to better counter the rapid emergence of mech that has accompanied 5th edition. (implied that Biovores will be viable)!
Release in 2010 Janurary 16th
Sited - http://www.belloflostsouls.net/2009/08/40k-rumors-tyranid-tidbits.html
The Shadow in the Warp is 12" range ability: roll psychic tests on 3d6 (all 3, don't discard the lowest), Perils of the Warp on double 1 or 6. Free for Hive Tyrant, Tyranid Warriors and Trygon Alpha.Pyrovore: Template is S:6 AP:4.
Synapse CreaturesUnits within 12 inches are fearless. No more Eternal Warrior.
Each Tyranid unit not in range of a Synapse creature has to pass a morale check or falls back to instinctive behaviour.
Melee-creatures move as fast as possible to the next enemy, while shooting creatures go for the next cover and shoot at the nearest enemies. What they do is said in their entries.
Weapon symbionts are no longer modified by the creature that wields it. There are heavy variants of most of them for the bigger creatures.
Venom Cannon: 3" blast now. They suffer a additional -1 penalty against vehicles. So, a glancing hit is - 3, a penetration - 1. So vehicles can now be wrecked with this weapon.
Heavy Venom Canon: S:9, same as above.
Scything Talons: One pair of tham grants rerolls on all 1's rolled to hit. Two pairs allow you to reroll all failed to hits.
Bonesword: Causes instant death, if the target fails a morale check after suffering a wound. If you bear two pairs, the morale check is made on 3d6.
Tentacle Whip: Reduce the initiative of all models attacking the user to 1.
Crushing Claws: D3 additional attacks.
These grant USRs.
Examples: Toxic Glands grant poisoned attacks (4+).
Adrenalin Glands grant furious charge.
An Injector grants Instant Death on each to wound roll of 6. There are many more.
Hive Tyrant, Alpha Warrior, Tervigon.
Named HQs: A special Hive Tyrant, A parasite-spreading winged horror.
Hive Tyrant: Initiative 6, WS:8. Starts of with a pair of Scything talons, a Tentacle whip and a Bonesword. May be given wings or heavy carapace (2+ armour save). May be given a Tyrant guard.
Hive Tyrant variant called the Swarmlord. Armed with 4 Boneswords (see rules above), and loaded up with special rules but costs more than a Land Raider.
May chose from 4 different psychic powers:
Mental Scream: All enemy units within 18 " have to pass a morale check. if they fail it, they suffer the difference between the roll and their morale characteristic as casulties with no armour saves allowed.
Lifeleech: One unit within 12 " suffers D3 S:3 AP:2 hits. For each casualty they suffer, the Hive Tyrant gains one wound, up to a maximum of 10.
Power 3: Forces a unit to pass a morale check or to fall back.
Power 4: A shooting attack.
Tyrant may be given special abilities, such as the ability to grant another unit outflank and +1 to reserve rolls.
Many weapon options available.
Special Hive Tyrant: WS:9. Invulnerable saves passed versus wounds inflicted by him must be re-rolled. He may give one unit within 18" Prerfered enemy, Furious charge or two other USRs.
Alpha Warrior: WS:6, granted to any unit of Warriors he joins.
Tervigon: Creates 3d6 Termagaunts with standard loadout each movement phase, even in close combat. If killed, gaunts nearby suffer heavy losses. It has its own psychic powers.The Horror "The Parasite of Mortrex": Winged hit-and-run monster. Every enemy unit outflanking may suffer casualties. The outflanking unit picks one model, and must pass a toughness test. If failed the model is removed and the Tyranid player gets D6 Ripper swarms.
The Horror does the same to victims he kills in assault.
Hive Guard: Unit size 1-3, BS:4 Weapons are 24" S:8 AP:4 Assault 2.
Lictors: 1-3 per FOC slot, acting together as one unit. Lictors deploy like Marbo. Grant +1 to reserve rolls. Deep striking units do not scatter if deployed within 6 inces of a Lictor, as long as it was on the table for at least one turn.
Ymgarl Genestealers: Biomorphable Genestealers. They may increase Attacks, Toughness, or Strength at the beginning of each assault phase. "Hibernation" rule: Pick a piece of terrain. When the Genestealers enter play, they are placed in the selected terrain. The unit may move, shoot and charge. Unit size: 5-10.
No Broodlord option. (he is now a troop choice!)
Zoanthropes: Unit size 1-3. Warp field grants 3+ invulnerable save.
Two psychic powers:
Warp lightning: S:6 AP:3 3 blast-Warp lance: 18" S:10 AP:2 Assault 1, lance
Special Zoanthrope "The Doom of Malantai": Leeches wounds with a powerful 5" blast shooting attack. S is equal to current number of Wounds, max of 10.
Death Leaper: WS:9, I:7. Deployed like a lictor, but may retreat and be replaced text turn. (I assume this is similar to the Eldar Swooping Hawks)
Hormagaunts: WS:3, S:3, I:5, A:2. Infantry. May be given poison and adrenalin glands. Unit size 10-30
Gaunts: Weapon is S:4 AP:5 Assault 1. For each 10 gaunts, one may be upgraded to a S:2 template that wounds against the target's Strength ~Sounds like tanglewebs return.
Warriors: WS:5, Many options. 4+ Armor save.
Genestealers: Mostly the same, but with less options. Cheaper than Grey Hunters, though. Armor save canot be increased. Infiltrate and Fleet.
Broodlord retains his statline, at a point cost of a Long Fang with a heavy bolter.
May have two psychic powers:
Confusion: Both players roll a D6 and add the Ld of a model chosen by the Tyranid player. If the Tyranid total is the same or higher, the enemy targeted model may not attack in this close combat phase.
Ability 2: Reduces the Ld of surrounding enemies by 1.
Harpies: Flying, Trygon-sized creature that acts as a bomber. It drops Spore mines on a unit it flies over. Monstrous creature.
Raveners: Two pairs of scything talons. May have a thorax swarm: a special weapon, with ammo chosen at the start of the game. Three flamer variants.
Carnifexes: Unit size: 1-3. Must have the same loadout. Cannot boost initiative, probably cannot improve armor past 3+. Gain +1 I when charging. Adrenaline glands give I:4 and S:10. Basic WS:3 S:9, W:4 2 pairs of scything talons, A:4.
Trygon: WS:6, S:6, W:6 A:6. Shooting attack: 12" S:6, AP:5 Assault 6. Deep Strike. Trygon cannot assault a unit he Deeps Strikes onto. Follows the same rules as Drop Pods, i.e. stopping within 1".
If upgraded to a Alpha Trygon, weapon becomes 18" Assault 12.
Tyrannofex: Walking weapon battery.
Fleshborer swarm: S:4 AP:5 Assault 20
Pyroacid spray: S:6 AP:4 template, used like the IG Hellhound.
Capsule cannon: 48' S:10, AP:4, Assault 2
Spore Capsule: Many units may purchase a Spore Capsule. Occupancy:1 Monstrous Creature, or 20 Infantry. Deep Strike. Disembarking unit may not move or assault. It may shoot.
STATLINE: WS:2 BS:2. T:5-6 W:3 A:3 S:6.Weapon: 6" S:6 Assault 6.
Sited - http://www.belloflostsouls.net/2009/08/40k-rumors-tyranid-tidbits.html
Venom CannonR:36 S:6 AP:4 Assault 1 Blast-1 modifier on the vehicle damage chart
Heavy Venom CannonR:48 S:9 AP:4 Assault 1 Blast-1 modifier on the vehicle damage chart
Barbed StranglerR:24 S:4 AP:6 Assault 1 Large Blast
Stranglethorn CannonR:36 S:6 AP:4 Assault 1 Large Blast
SpinefistR:18 S:4 AP:5 Assault X(X= bearer's number of attacks), twin-linked
FleshborerR:18 S:4 AP:5 Assault 1Sting BlasterR:12 S:5 AP- Assault 1
Spike BlasterR:18 S:5 AP:5 Assault 4
Texorin Bug 3 fire modes, may be fired additionally to all other weapons:
Template S:* AP- Assault 1, wounds on 2+ vs. non-vehicles
Template S:5 AP:5 Assault 1-Template S:3 AP:6 Assault 1, Rending
Death BlasterR:18 S:5 AP:5 explosive
Toxin Sacs: ALL units may buy these. Grants Poison attacks (4+)
Adrenal Gland: ALL units may buy these. Grants Furious Charge
Spore Launcher: Big bugs only. Grants Frag granades
Injectors: To-wound rolls of 6 cause the loss of all wounds instead of one
Flesh Hooks: R:6" S:5 AP- Assault 2
Toxic Blood: When the model loses a wound in assault the model causing the wound must pass an I check or lose a wound with no armor save allowed. Vehicles suffer a glancing hit on a 4+ Toxic Miasma: Enemy models in assault range pass a T check or lose one wound with normal armor saves allowed
Lashwhips: All enemy models in assault are reduced to I:1
Chitin Upgrades: From 6+ Armor save to 2+, with several variants
Boneswords: A model suffering a wound to the weapon must pass an Ld test or is killed outright. If the bearer has a pair of Boneswords the Ld test is made on 3D6.
Scything Talons: Reroll to-hit rolls of 1 in assault, models with a pair of talons reroll all failed to-hit rolls
Rending Claws: Grant Rending USR in assault
Crushing Claws: Model I is lowered to 1, +D3 Attacks
Regeneration: At the start of each turn the model regains a lost wound on a 6
Wings: Model counts as Jump Infantry
Sited - http://www.belloflostsouls.net/2009/12/40k-rumors-weapons-of-hivemind.html
Unfortunatly i cant find anything about the Mawloc, but it is supposed to be like a big Ravenor.
I will leave this with you and let you decide on the future, remember these are still rumors and until the Codex comes out treat them as such. Enjoy