Predecessor Builds > Dekker > Dekker Mid (Could also be used for Offlane)
This build is for agro Dekker usage, focused on ability haste, mana, and damage, all at once! Azure core is usually a must for the first item because of the mana stacking you must do. Astral can be swapped with Megacosm if it is more of a battle of poke than team fighting in the early to mid-game. But, for me, alteast, 9/10 Astral is the best because of the mana, ability haste, ability power increase when doing your RMB to Q to R combo, and the potential to launch 2 ults in one early to mid-game team fight is enormous. If you need some durability against physical asap, go timewarp. Really, this second item is a flex item; situational by each comp. Though, if you can better your ability to escape every situation with Dekker, (ie ganks, lost team fights, being caught out, etc), Astral will most likely be your best choice.
You can see from my matches that I usually go this order of items, with a successful win rate on top of this as of the recent 20 matches. Though, to use this optimally, your mechanics with Dekker will really be the end all of you being successful in mid, or offlane as well. Lv1 harras to op with your RMB, Lvl 2 harass with a RMB to Q combo. Then, take your river buff asap and rocket boots back onto the ledge, and immediately get back to laning. Recommend backing asap when you reach enough gold to get your alch rod for stacking mana stacks. From there, continue to harass, push, and gank your duo or offlane.
If you would like to see how Dekker should be played in the mid, off, or even support role, I usually stream on Twitch and one-trick her. My past streams are also on there to review. My Twitch is simbaNA, or you can use the link here -> https://www.twitch.tv/simbana
Good luck, and happy jumping :)