My SB is full of versatile cards that fill different scenarios, so my 15 card sideboard is much bigger than it seems.
Fulminator Mage Greatest land destruction ever. Can beat on opponent if needed and can be sacced in response to removal or blockers if need be. Against tron is sacced immediately.
Ancient Grudge Comes in vs affinity and other decks that run too many artifacts for Kolaghan's Command/Abrupt Decay to handle.
Shatterstorm Really puts the nail in the coffin for affinity, mainly to deal with Etched Champion, who's just a real problem.
Languish Board wipe for those aggro and midrange decks. To be upgraded to Damnation soon.
Engineered Explosives I've flip flopped back and forth with using this. It can be cheap and is very versatile with killing different permanents.
Night of Souls' Betrayal Our token killer of choice. It can also shut some creature decks out of the game after you stabilize. Nukes Lingering Souls, mana dorks, hurts affinity, sword foundry, locks infect out of the game, etc.
Olivia Voldaren Really shines in aggro and midrange matchups. Kills things and puts on muscle, plus she flies. Also kills thopters.
Thrun, the Last Troll Added as a concession of the inevitable rise of the blue decks. These decks just can't handle Thrun.
Grim Lavamancer Great repeatable removal that stops many decks and definitely helps when I'm on the 'Kill Everything' plan.
Duress great additional hand disruption against control, combo and burn.
Painful Truths I feel like this is the best option for card advantage in the current meta. It's bad on t3, but good later on. Outpost Siege dies to Nahiri, the Harbinger, Chandra, Pyromaster doesn't do enough IMO and Ob Nixilis Reignited is too expensive for me.
Crumble to Dust Added a 4th LD spell, because Big Mana decks are about 20% of the meta currently and another spell to hurt them wouldn't hurt. Also considered Boil.
Kitchen Finks This guy generates alot of card advantage as opponent tries to remove it. Also fairly good in combat.