I have been testing Mardu since rotation and in this deck I am incorporating the main pieces of the decks Brad Nelson and Melissa DeTora ran in recent events, along with tweaks to fit the meta in my area as well as address some problems I anticipate as the meta continues to involve.
With 11 sources of scry, the idea is to position the deck to be as fast as possible in game one, getting a Seeker out T2, Hordeling Outburst or Rabblemaster T3, then a Butcher on T4 and roll, using Crackling Doom to deal with big threats and Chained to disrupt tempo (Magma Jet also helps here and the scry 2 can be huge).
Once you get threats with Butcher and either tokens or Rabblemaster in play, hold God's Willing to protect Butcher or Rabblemaster until you can raid into Wingmate Roc or get Sarkhan out. I will be careful not to haste Butcher when he hits if they can remove him, so I don't lose valuable tokens. In fact I will always go all in first and sac creatures for lifelink and/or haste after blockers are declared.
Matchups
Mono Red, or any aggro
In - 3rd Magma Jet (extra cheap removal, scry huge here), Anger of the Gods (of course), Elspeth and End Hostilities, so if I have to go to deep water I can.
Out - Crackling Doom (no real fatties so rely on Jet and Chained), Sorins and Sarkhans. Doom is an easy choice here, Sarkhan and Sorin, not so much, but I really feel better with a mass removal 5 drop than a 4/4 Dragon 5 drop. Also once I weather the early blitz, Butcher and a token give me the life gain needed to stabilize.
Against R/G, Temur, Green Devo I will go full control.
In - Elspeth, Hushwing Gryff (for Hornet Queen) Anger if needed for Mana dorks, Utter End, End Hostilities and Read the Bones.
Out - Seeker, Rabblemaster, Magma Jet, Gods Willing (if no burn threat) and a couple of Hordling Outburst if I need a full 14 card swing. I can get by with the 2 Outbursts here, since I will get tokens from Elspeth if I play it right and get the game deep.
B/U, W/U control
In - Hushwing Gryff, Elspeth, Read the Bones.
Out - Crackling Doom, Chained to the Rocks.
Basically get rid of 7 dead cards here for 7 that can help late. I will keep Magma Jet in only for the scry ability.
Abzan
In - Hushwing Gryff, really beside Hornet Queen, the main reason I even have this card is Siege Rhino. Shutting down that life swing goes a long way to beating Abzan. Elspeth since I am dropping Outburst and Utter End is a definite here for Planeswalkers. (Situationally Anger and End Hostilities may make an appearance too depending on style)
Out - Magma Jet, Chandra, Hordeling Outburst. If I bring in Anger for Mana Dorks in an Aggro situation, I would drop Seeker, but usually this is not an issue. If End Hostilities is needed I keep Chandra and drop Seekers.
A few different options against Abzan depending on the style they play.