Not intended for newer players, this is a very glass cannon play-style, oriented around burst, distancing, and kill security (or mid bullying)

Crest

The Crest is tricky, and obviously depends on a lot of factors. "Tranquility" is actually tangible due to the huge amount of MP you'll be building, or the tried and true "Reclamation" to pair with your escapes (and teams) since we're going Glass Cannon with this build.

Core Items

Instead of buying Marshal or Req first, and hoping duo isn't bullied or that your Carry is having a bad day, we're going to first build into "Timewarp".
Great first item as it's the only card that provides relatively high MP, ability haste, first and second stage mana regen cards, and has a full build passive that reduces CD on abilities. Being as that ranged stun is your bread and butter, it'll pay off to have regen to pair with those constant stuns.
This build will further focus on individual strengths and what the -person- can provide for the match, vs their cards. Part of the problem with building support cards is their stats are usually -under- sub par, so if duo is controlled, or is losing, at that point you're at a larger deficit as you're using 1/2 a card essentially.

From here since our first card doesn't have much for survivability, we're going to push into "Wraith Leggings".
Again with the rage mage cannon support build we're pushing into, we still need some mobility since we don't have sustain, so to pair with the theme, (and Dekkers passive jump/boost) we're going to get a speed boost on hit. This is also a great card as it has early +15 pen (to pair with the reduced ability cooldown from Timewarp) and extra damage on heros below 40%. Early game because there's not a ton of damage going out, this is particularly great passive to have with a reduced GCD tic from Time.

Mid Game and Flex

The next cards are really dependent on how the game is being played out. If you're bullying then it'll be great to build into "Combustion". The on hit is nice damage, and great AoE for Dekker clear (yea I know how it sounds, but you can't not have it at least in consideration. It's better to be over, than under-prepared). Plus the card has great synergy with Timewarps CD reduction for it's "Pyromaniac" passive, and it's magic pen is a nice touch to stack on top of Wraith Legging's.
If you're -being- bullied, then another nice touch is "Spellbreaker". Mid range damage, but provides a bit of magic armor (the theory here is to focus a bit on ranged defense as Dekker's jump/boost and Wraith Leggings should be enough to give you enough distance from melee) and obviously a spell shield from big ranged hits. It's also a nice touch to have the "Malefic" passive of getting a 20% total magic damage bonus (makes up for the mid core MP).

Flex

If it's a relatively balanced match, but enemy healing is a factor, we can obviously sub in "Tainted Scepter". Not the strongest of all, but for ranged glass cannon build/play time, it gives nice damage, magic pen, and a passive "Malice" that stacks nicely with the bonus damage of "Wraith Leggings" if you "accidentally" get a kill ;p (I would recommend building it third, followed by "Combustion" instead of current top build, so that you can maintain constant impact damage, and lane control).
If the enemy team seems to notice what you're doing, and consider you a threat, (or has heavy melee and you prefer to lean on the safe-side of playing but still want to push out some damage numbers for cheap) there's "Golems's Gift". An under appreciated card that gives at max of 100 MP and 60 total physical armor to help with being bursted down with such little HP / amor. (I would recommend building this, again as third, followed by "Spellbreaker" if you're being bullied)

End Game

This is the fun stage -- you can build to be constant aggro and annoying by going "Megacosm" and providing tics and AH (ability haste) to spam and ram. Or you could go the bruiser route, pull it out, and lay "Oblivion Crown" down. At this point you will be, essentially, a full mage doing 1/5 - 1/3 carry's HP on hits depending on the situation.

Slay