Even theoretically mono-coloured decks featured the incredibly powerful scry lands over the course of the weekend. Combining fixing one's mana base with small but incrementally powerful card selection lets players smooth their draws, dig for answers in desperate situations, and access powerful and flexible options from their sideboards. The trade-off in speed has been mitigated by the Return to Ravnica-block duals, and even aggressive decks seem happy to trade a peek into their futures in exchange for a comes-into-play-tapped dual land.
4. Boros Charm
If Boros Charm isn't the Mixmaster of the burn player's kitchen, we don't know what is. Not only does it slice and dice, but it comes with built-in safety features that protect your creatures from unwanted Wrath effects. Like all appliances, it does come with a rarely-used 'bonus' mode in the form of double strike, but two out of three abilities for the low, low cost of 2 mana in easy, single-tap instalments is enough to keep players coming back for more.
There's little about Erebos that's not been said, so let's just recap and move on. He stops your opponents from gaining life - surprisingly relevant in a world dominated by Blood Barons of Vizkopa and Gray Merchants of Asphodel -, he draws you cards in a pinch and he plays very well with others. If he's not in your 75, you might be doing it wrong.
Ken Yukuhiro played one of the most interesting decks of the GP, a U/B heroic deck featuring Tormented Hero, Agent of the Fates and a bevy of tricksy Blue spells, most notably Hidden Strings. Ciphering this powerful sorcery onto a creature let Yukuhiro demolish defences, trigger his heroic creatures regularly, and generally mess with his opponents' game plans. If you've been staring wistfully at Hidden Strings, wist no more and consider shuffling them up at your next FNM.
Another card that caught more than one player by surprise, Yuuya Watanabe used this to great effect in his semifinal matchup, getting three into play in games 2 and 3 against a burn player. The 'lucky charms' cycles that old-school players will recall started with Throne of Bone and friends have been through many iterations, this is definitely one of the most impactful. Gaining life off lands and spells isn't too bad a deal, and as Watanabe-san showed, if you get multiples into play, things can start getting a bit silly.