The "Spiraling Doom" deck is an extremely reactive deck: most of
your decisions will depend on what your opponent is doing and how your
opponent is trying to win the game. The key card in your deck is
Birthing Pod, which lets you sacrifice a creature to go get a slightly
more expensive creature out of your library. Once you have Birthing Pod
on the battlefield, use it to find the perfect creature for every
situation! If you need to kill a creature, look for Skinrender. If you
need to deal with a powerful artifact, enchantment, or land, find your
Acidic Slime and take it out.

If your opponent's deck relies on attacking you right away with
small creatures, stay back on defense. Creatures like Young Wolf,
Strangleroot Geist, and Viridian Emissary make perfect blockers. All of
them give you added benefits if they trade with your opponent's creature
in combat. Viridian Emissary replaces itself with a basic land, helping
you to cast your more expensive spells like Myr Battlesphere and
Bloodgift Demon earlier, and the other two come back to the battlefield
stronger thanks to their undying abilities.

If your opponent decides to sit back and wait, you can often force
the issue. Attack with Strangleroot Geist or Young Wolf when your
opponent has several 1- or 2-toughness creatures. Blocking them won't be
an attractive option. After combat, cast a Mortarpod and equip it to a
creature. Then if you need a blocker, sacrifice that creature and it
will return to the battlefield ready to block. If you have Skinrender
instead, you can just kill your opponent's biggest creature and scare
off the rest with the 3/3 blocker.

Because of Birthing Pod, your main deck includes at least one
creature for most situations you can expect to face, but your sideboard
lets you focus even more. Against opponents playing for the long game,
Despise and Distress can prevent them from casting their best spells.
Gravedigger and Myr Sire are more creatures that are good against
aggressive opponents. Dismember can also buy a lot of time.

Birthing Pod is a flexible card that empowers a variety of
strategies, but for the most part, it's all about creatures. If you want
to customize your deck, look for creatures with "enters the
battlefield" triggers and "dies" triggers. The Dark Ascension card
Geralf's Messenger has both. Or you could look for creatures that punish
specific decks. If you're facing lots of decks with artifacts, Oxidda
Scrapmelter can be a valuable part of your Birthing Pod toolbox. If
you're expecting lots of creature removal, Sheoldred, Whispering One is a
great way to bring your creatures back from the grave.