Remember to +1 Upvote!
| | The colors of necessity when it comes to trying to exploit the new mechanic -- Exert.
Negating the Exert cost with Vigilance really makes this deck what it is. Gaining all the benefits with none of the negatives is cheating the mechanic but who cares. Giving things Haste and Doublestrike are also mischievous ways to win in combat and both are major sub-themes within this deck. All this adds up to what is an immensely fun to play deck.
Midrange decks sit in the sweet spot between aggro, control, and combo. A jack-of-all-trades archetype so to speak. With efficient beaters and effective tempo plays it's just hard to combat this decks power.
Suggestions and comments on what removal to add, if any, would be greatly appreciated.

Glorybringer (Promo) | Art by Grzegorz Rutkowski
Glorybringer
+ Arlinn Kord
(giving it Vigilance for Exert) is a hard to answer curve. T4 Arlinn, T5 Glorybringer. It flys in for a hasty four damage and potentially kills something in the process. This is a nice tempo play that's hard for mostly everything to answer and bounce back from. This combo quickly ends most games.
Arlinn ability is also very relevant to
Combat Celebrant
for Vigilance also works in favor of it's Exert cost. Plus giving it Haste goes a long way to making this card even more playable. It dies to every removal in Standard with just 1 toughness but if you can use it once by giving it Haste the turn it enters then it becomes more of a playable option.
Lightning Runner
is a similar card but you would need a way to get the Energy to gain full benefit of playing it. Aside from the steep mana cost I do like it solely for it's Doublestrike and Haste -- even if it is a mere 2/2 to begin with we got plenty of anthem and pump effects to play around with that'll get it up to par.
Always Watching makes non-tokens +1/+1 and passes around Vigilance to all which is the Exerts' best friend. These two mechanics together are deadly.
Onward / Victory
This card fits what the deck wants to do. It can give your creature more power, then be used to give it double strike. +X/+0 is a good effect when paired with any of the creatures already with doublestrike or be paired with an already activated Electrostatic Pummeler to further pump it's power towards the sky. Then you realize you can can re-cast it so to speak giving anything doublestrike. So many ways to obtain doublestrike in this build.
Electrostatic Pummeler
It pairs well with
Lightning Runner
thanks to
Eldrazi Displacer
to give us that Energy generation engine we need. Itself though is a Energy Dump that can be extremely lethal. Especially when given Haste considering you might have enough Energy to activate it's self-pump twice in a turn before they know it you have a massive threat.
Pair that with Larger Than Life and other pump spells and you've got a high end beater. Then again you might not even need to attack if you got this...

Peema Aether-Seer
Cast on a turn you pumped one creature to insane power and you insta got enough Energy for a
Lightning Runner
or a couple Electrostatic Pummeler activations.
Needle Spires
I love me some Doublestrike. This Boros | land creature might not offer much as a mere 2/1 body but it beats hard with all the pump effects we play. Once you got the lands for
Sylvan Advocate
it'll be boosted to a 4/3 and that's 8 damage with the double strike which isn't bad for a surprise attacker they more than likely forget about until it's too late.
Uncaged Fury also grants doublestrike.
Channeler Initiate
is in the sideboard for now but it's got some interesting plays within this deck. Great for Mana-fixing in any 3-color deck but also alongside
Eldrazi Displacer
it can be flickered and reloaded with -1/-1 counters to keep tapping it for any color of mana. Even when they run out it's not a bad creature left behind as a 3/4 that'll be buffed from other effects.