Here is the Gnawbomb list that has done me well the last couple of tournaments. I placed 3rd and 5th with it.
It's a really solid list but it does rely on dice rolls. For the most effective gnawbomb you need to cast MMMP, Dreaded Skitterleap and Skitterleap.
The idea is that you cast MMMWP on the Stormfiends, then Dreaded Skitterleap the Deceiver to a piece of terrain then turn it into a Gnawhole. Then Skitterleap the Arch Warlock over to the Gnawbomb. In the movement phase send the Stormfiends through the Gnawhole. If you're facing a combat army, then pop up 40 clanrats as a screen around the fiends using the Warp Grinder.
The Gutter Runners come in off the board edge to harass the flank. This can be done on the opposite side of the table to the Gnawbomb so your opponent has to divide his attention. If he doesn't take out the Gutter Runners they will cause trouble.
That's the general idea, but it does require different tactics in some situations. Deployment generally has your heroes grouped together (and you need them all for the trick to work properly) so something like a Stormcast comet can ruin your day.
Allegiance: SkaventideLeadersVerminlord Deceiver (320)- General- Command Trait: Shadowmaster- Artefact: GnawbombArch-Warlock (160)- Lore of Warpvolt Galvanism: More-more-more Warp Power!Grey Seer (140)- Lore of Ruin: SkitterleapBattleline40 x Clanrats (200)- Rusty Blade- 2x Standard Bearers- 2x Standard Bell Ringers40 x Clanrats (200)- Rusty Blade- 2x Standard Bearers- 2x Standard Bell Ringers20 x Clanrats (120)- Rusty Blade- 2x Standard Bearers- 2x Standard Bell RingersUnits6 x Stormfiends (520)- 2x Windlaunchers- 2x Ratling Cannons- 2x Shock Gauntlets20 x Gutter Runners (200)1 x Warp-Grinder (80)Endless Spells / Terrain / CPsBell of Doom (40)Total: 1980 / 2000Extra Command Points: 0Allies: 0 / 400Wounds: 182
Here's the list that did really well for me last year and consistently placed in the top 5 at events.
It used to have 20 more clanrats in it but points increases put a stop to that.
This one is less of a single strategy focused list and is designed to play the objectives with bodies while Thanquol and the Warbringer are the ones doing the damage.
Allegiance: SkaventideLeadersVerminlord Warbringer (280)- General- Command Trait: Brutal Fury- Artefact: Things-BaneThanquol on Boneripper (400)- 4 Warpfire Braziers- Lore of Ruin: WarpgaleGrey Seer on Screaming Bell (240)- Lore of Ruin: Death FrenzyGrey Seer on Screaming Bell (240)Battleline40 x Clanrats (200)- Rusty Blade- 2x Standard Bearers- 2x Standard Bell Ringers40 x Clanrats (200)- Rusty Blade- 2x Standard Bearers- 2x Standard Bell Ringers20 x Clanrats (120)- Rusty Blade- 2x Standard Bearers- 2x Standard Bell RingersUnits40 x Plague Monks (280)- Foetid BladesTotal: 1960 / 2000Extra Command Points: 0Allies: 0 / 400Wounds: 191