How are people beating Tyrant of Valakut?

Check General Discussion, there are a ton of deck builds there for this challenge (some of which should be posted here for posterity). For myself, I have beaten it with Ob Nixilis and Liliana, both abusing Demonic Pact. Add in some hand destruction, creature removal, and other Planeswalker tricks, it is pretty easy.

Here are my two decks:
Ob Nixilis -

Demonic Pact
Shrine of the Forsaken Gods
Sunken Hollow
Vampiric Rites

Transgress the Mind
Alchemist's Vial
Grip of Desolation
Grave Birthing

Gnarlroot Trapper
Bonded Construct

Wipe out their hand, delay and destroy creatures, until you get 15 loyalty. Then role with the damage, getting 16 if you have Demonic Pact and guaranteeing 8 when they draw. Also do 24 damage if you activate Vampiric Rites, and 16 if you use the first ability. Alchemist's Vial delays creatures, and does 8 damage with the card draw. Grave Birthing puts a chump blocker, ingests, and draws a card, doing 8 damage.

Liliana -

Shrine of the Forsaken Gods
Demonic Pact

Grave Birthing
Infinite Obliteration
Grip of Desolation
Dark Petition

Fathom Feeder
Ulamog's Despoiler
Sludge Crawler
Blight Herder

This is a hand-deny / ressurection deck, that once you have lockdown with Demonic Pact and hand discard, you pay for your expensive creatures and/or resurrect them with ability 3 or Dark Petition.

I use Gideon I with Consul's Lieutenant for the First Strike ability. Pair this with Gideon's third ability to get Regenerate 5 and some other pump spells and you can hold on for the win.

The core concepts for the deck are:

-First Strike creature
-Pump spells/supports (so that you can first strike anything 20 health or higher)
-Prevent damage for when you can't first strike in one go
-Gideon's third ability to deal with the direct damage your first striker will be taking (keep in mind you may get hit with the ability and he may play himself as a card too meaning in one turn you can take 12 damage to all your creatures plus yourself)
-Lifelink to restore your health from all the direct damage.

Strategy is to get loyalty for third ability fast. While charging up Consul's Lieutenant and pump spells/supports to drop a beast on the board. Just make sure you don't give him Vigilance unless he's ready to drop the enemies with First Strike unless you can protect him with Enshrouding Mist.

Be aware that the enemy may play some removal spells like Crush of Tentacles so you may need to start from scratch once you get going.