While this isn't a guide, you might find it helpful.
PRIMARY:
Spectral Wounds - Get it and 6-slot it quickly. You want to put damage enhancements here, to help increase damage output (that isn't spectral and "heal" back).
Blind - Another great power, as this sets up containment for your Spectral Wounds.
Deceive - Another great power, as this is a "hold" when used on a solo enemy and a "help me while I defeat the group" power when multiple enemies are around. Also, it doens't produce any agro for you, so you can use it on enemies near glowies (interactive objects) and then stealth click the object!
Flash - While you can hold off or skip this power entirely, this is a nice AoE hold (on slow recharge) that combines with Blind to hold bosses. Since you'll probably build for recharge, this power only gets better in that combination.
Superior Invisibility - A nice "stealth" power, and a good place for a LoTG +Rchg enhancement. This is one of the best stealth powers in the game, but it only affects you.
Group Invisibility - Another nice stealth power, and this affects any teammates near you (your pets included)! While you might not want to take both invis. powers, your playstyle will dictate one over the other. Also, another place to slot a LoTG.
Phantom Army - Ok, this is your defining power. Take it and 6-slot it ASAP. You want damage and recharge! Add in accuracy and possibly EndRdx later (through IOs, preferably). This is also why you want your build to be focused on recharge!
Spectral Terror - Another great power, as this is your AoE fear. It will help mitigate incoming damage, and is a great opening power when PA is down.
Phantasm - Your final pet in your primary. Take it and slot it with 5 or 6 slots.
SECONDARY:
Twilight Grasp - You get it automatically, and it's a very powerful heal...when it hits. It also debuffs ToHit! And Regen! Slot it up as you work toward 50.
Tar Patch - If you skip this, why did you pick /Dark? This is your slow and Res debuf super power! And, with enough recharge, can be stacked on itself!
Darkest Night - A great power early on, and toward the end when you're fighting AVs and GMs. On teams, I only use it on hard targets. Ok, I only use it on hard targets even when soloing. You can put this one off for awhile if you'd like.
Howling Twilight - This power is both an AoE rez and a massive -Regen power (and it disorients minions and automatically hits!). Use it as such! Against large groups, it's great. Against hard targets, it's great. When you're PUG really isn't very good, it's great!
Shadow Fall - Yet another team stealth power, and this one adds in +DEF and +RES (the others offer +DEF)! I took it at 22 and keep it running continually...unless I need to escort some poor NPC around. For that reason, I try and skip escort missions!
Fade - Another team +DEF, +RES power! Actually, this will work on anyone around you, even non-team players! I wouldn't skip this power either.
Soul Absorption - +Regen, +REC, and foe -ToHit PBAoE. I've seen several builds that skip this power. I took it, but it's possible to skip it. I usually use it after my PA or a tank has drawn all the agro, then I move in and fire it off. If you have a large group of bad guys, the buff is amazing. If you only face small groups, it is probably not very useful.
Black Hole - Feel free to skip this power. It's useful solo, but on a team too many people just don't understand it. They will burn all their END fighting a target that continually produces "UNAFFECTED" text when they attack...sigh!
Dark Servant - Take it, slot it, and love it! The only thing to remember is that you will need to resummon him every 4 minutes. While I don't understand or agree with this, it isn't nearly as bad as it might seem.
I hope this helps! 
I love my Ill/Dark 'troller! Of course, I've wanted one since I2! 
7+ year vet with too many alts to list...
This post will be two fold, maybe this will give the OP an idea of powers to take and not to take. and i 100% agree with Feint of Heart.....a few quirky things on this build, i have respec'd this guy at least 4 times to get to where i am at, and BOY AM I HAPPY.....ill/dark was such a blast to level up.....i suffered mainly without Def and had some hard times, when my PA wasnt perma.....
So notes:
1. Only toggles i run are Shadow Fall, Hasten (set it for auto fire), Combat Jumping, Maneuvers and Shark Skin. Also, click fade every time its up......
2. Its not shown on here, but i put that new Overwhelming Force: KB -KD IO in Water Spout, mainly cause i forgot the description was wrong in my haste and it does KU not KB...BUT, seems to work well anyways, sometimes you can see the enemy get pinned down and just water spouted to death, its quite amusing....
3. In the end game i took Barrier, so with this build, clicking fade every time its up (its perma), and with Barrier at its weakest, you are softcapped for Ranged DEF and have over 50% S/L res....highly survivable, since perma PA hooks it up!
Hope this helps out with power selection n slotting n junk, and i just wanted to share this build cause i am having a blast with it, after i didnt think it was possible to make the guy better!
**Also not to get off subject, but should i have put the KB-KD IO in phantasm or PA? thoughts?**
Hero Plan by Mids' Hero Designer 1.957
http://www.cohplanner.com/
Click this DataLink to open the build!
Illusion of DaSlaya: Level 50 Magic Controller
Primary Power Set: Illusion Control
Secondary Power Set: Darkness Affinity
Power Pool: Flight
Power Pool: Speed
Power Pool: Leaping
Power Pool: Leadership
Ancillary Pool: Leviathan Mastery
Hero Profile:
Level 1: Spectral Wounds -- Decim-Acc/Dmg/Rchg(A), Decim-Acc/Dmg(7), Decim-Dmg/EndRdx(9), Decim-Build%(9), Decim-Dmg/Rchg(11)
Level 1: Twilight Grasp -- Dct'dW-Rchg(A), Dct'dW-Heal(34), Dct'dW-Heal/EndRdx(34), Dct'dW-Heal/Rchg(36), Dct'dW-Heal/EndRdx/Rchg(36)
Level 2: Blind -- BasGaze-Acc/Hold(A), BasGaze-Rchg/Hold(11), BasGaze-EndRdx/Rchg/Hold(13), BasGaze-Acc/EndRdx/Rchg/Hold(13)
Level 4: Tar Patch -- TmpRdns-Acc/Dmg/Slow(A), TmpRdns-EndRdx/Rchg/Slow(5), TmpRdns-Acc/Slow(45), TmpRdns-Dmg/Slow(45), TmpRdns-Rng/Slow(45)
Level 6: Flash -- SWotController-Rchg/Dmg%(A), SWotController-Acc/Conf/Hold/Immob/Sleep/Stun/Fear/EndRdx(7), SWotController-Acc/Conf/Hold/Immob/Sleep/Stun/Fear/EndRdx/Rchg(15), SWotController-Acc/Conf/Hold/Immob/Sleep/Stun/Fear(15), SWotController-Conf/Hold/Immob/Sleep/Stun/Fear/Rchg(17), SWotController-EndRdx/Rchg(17)
Level 8: Darkest Night -- DarkWD-ToHitDeb(A), DarkWD-ToHitDeb/Rchg(39), DarkWD-ToHitdeb/Rchg/EndRdx(39), DarkWD-ToHitDeb/EndRdx(39)
Level 10: Howling Twilight -- Stpfy-Acc/Stun/Rchg(A), Stpfy-Acc/Rchg(36), Stpfy-EndRdx/Stun(37), Stpfy-Acc/EndRdx(37), Stpfy-Stun/Rng(37)
Level 12: Deceive -- CoPers-Conf%(A), CoPers-Conf/EndRdx(23), CoPers-Conf(27), CoPers-Conf/Rchg(27), CoPers-Acc/Conf/Rchg(29)
Level 14: Superior Invisibility -- LkGmblr-Rchg+(A)
Level 16: Shadow Fall -- LkGmblr-Rchg+(A), LkGmblr-Def/EndRdx(42)
Level 18: Phantom Army -- ExRmnt-Acc/Dmg(A), ExRmnt-Dmg/EndRdx(19), ExRmnt-Acc/Dmg/Rchg(19), ExRmnt-EndRdx/Dmg/Rchg(21), S'bndAl-Build%(21), S'bndAl-Dmg/Rchg(23)
Level 20: Fade -- LkGmblr-Rchg+(A), RechRdx-I(25), LkGmblr-Def(48)
Level 22: Fly -- Empty(A)
Level 24: Hasten -- RechRdx-I(A), RechRdx-I(25)
Level 26: Spectral Terror -- Abys-Dam%(A), Abys-Acc/Fear/Rchg(29), Abys-EndRdx/Fear(31), Abys-Fear/Rng(31), Abys-Acc/Rchg(31)
Level 28: Soul Absorption -- Dct'dW-Rchg(A), Dct'dW-Heal/Rchg(42), Dct'dW-Heal(46), Dct'dW-Heal/EndRdx(46), Dct'dW-Heal/EndRdx/Rchg(46)
Level 30: Combat Jumping -- LkGmblr-Rchg+(A)
Level 32: Phantasm -- ExRmnt-Acc/Dmg(A), ExRmnt-Dmg/EndRdx(33), ExRmnt-Acc/Dmg/Rchg(33), ExRmnt-EndRdx/Dmg/Rchg(33), SvgnRt-Acc/Dmg(34)
Level 35: Maneuvers -- LkGmblr-Rchg+(A), LkGmblr-Def/EndRdx(50)
Level 38: Dark Servant -- BasGaze-Acc/Hold(A), BasGaze-Rchg/Hold(40), BasGaze-EndRdx/Rchg/Hold(40), BasGaze-Acc/EndRdx/Rchg/Hold(40)
Level 41: Water Spout -- Amaze-ToHitDeb%(A), Amaze-Stun(42), Amaze-Stun/Rchg(43), Amaze-Acc/Stun/Rchg(43), Amaze-EndRdx/Stun(43), Empty(48)
Level 44: Shark Skin -- S'fstPrt-ResDam/Def+(A), GA-3defTpProc(48), Aegis-ResDam/EndRdx(50), ResDam-I(50)
Level 47: Summon Coralax -- SvgnRt-Acc/Dmg(A)
Level 49: Hibernate -- RechRdx-I(A)
Level 2: Swift -- Empty(A)
Level 2: Health -- Mrcl-Rcvry+(A), Numna-Regen/Rcvry+(5)
Level 2: Hurdle -- Empty(A)
Level 2: Stamina -- P'Shift-End%(A), EndMod-I(3), EndMod-I(3)
Level 1: Brawl -- Empty(A)
Level 1: Containment
Level 1: Prestige Power Dash -- Empty(A)
Level 1: Prestige Power Slide -- Empty(A)
Level 1: Prestige Power Quick -- Empty(A)
Level 1: Prestige Power Rush -- Empty(A)
Level 1: Prestige Power Surge -- Empty(A)
Level 1: Sprint -- Clrty-Stlth(A)
Level 2: Rest -- Empty(A)
Level 4: Ninja Run
Level 50: Agility Core Boost
Level 50: Barrier Invocation
------------
Code:
| Copy & Paste this data into Mids' Hero Designer to view the build | |-------------------------------------------------------------------| |MxDz;1507;712;1424;HEX;| |78DA65945B4F13511485CFB453B0B448B15C85CA0062B996567D274AD5082D9090F| |8A4E204A630719C69DA62E44991E85F40A289B70808C64735FE0EA3261AC50BC617| |B55EDEC7DDD9AB94A4139A6FBA387B9D75F6EC4EF24ADCFFF4D4E2909002C3869AC| |D4E0D5B662E63198696F124D5597D5AD0153C6D18F359DD32152BA5C4D549435D50| |2B49EF2C2D2ED6458A4B8B42FBAE35C7E753A9485CCD5C3435DAE9582AA59B7A6E4| |1F8262C2A3C69E8B373B92AE77E32AD69337EE736A1A969DD9CAD297E99D132D939| |3DAD9C48EBD391B8754937D59C95994A6897753537A79A5349359BD3320B4D942F4| |C9FBB92C065CBE276419445C53273CF2DF00EB36A85B9D5B8AB66820C62B2681F07| |47999D49708C798FC05BD96EE9954B8810F9BD66FADF806F999FC8DF0D7FF713AE9| |73799FD6BE03AB8C17C40F0708DC7B3E976B48AC7CCBD1BE02A33B006AE333FD37E| |95C856F9CCE568879E832FC097CC2FB4D68B6CDE259CF12AF3E0357011BCCEBC4FF| |0A1C6A7B24FC305E6FEB3E03966EB79E643AAA9E61A515DCF3E5F69EF1AA789B654| |03AD2750A0573C22D4E2FCB579F6D8F71BFCC3ACFB0B0E23C310739B7C83ECEB0AC| |2B7A94F38BE8375ECEFA306D5234FBD4D97E820A511691A9DD5C52A59AC92DE8C13| |376FB163EB47E681F7E007F01DF31BA5687166C4965B30553D98A2014CD700A66B0| |053D54019429C418490BC30206DD8BB0D9D50D009059D50D089F63CE7AD259F0E9C| |A5033E3174F63BE5EAC274746172C398DC3026378CC95DA281EAC653E81EE73D7A4| |698BDA360021C630E3ADDBC41957D9CC0DD57682BB90D1EE6F98C453949AC9F9FC9| |4D92237816913C6BDB7E21A2D0A278763FAAE83787EE48CE2EBF4A8A248D48CEAF5| |93EC3E7FD59B63A5F525CD232A77529EC5D64ABBCF32EA0BF4255A8A4D8BD65FF8D| |9629B132E5489972B44C49EC56BC9C6D42DE79C7E004DEC0CE9BC4FED7408B70BF1| |22CDDFF07F2B309E0| |-------------------------------------------------------------------|
Phanty, definately phanty. I notice his KB much more than PAs. Of course, my priorities for those precious new toys are Bonfire 
i hear you on that Hextor...my Fire/Rad is chomping at the bit for that IO.....he is only 42 and this one was 50 so i figure, ahh both could use it lol....*hope i get another*
Hey all
Just rolled a Illusion/Dark controller and I am loving it, the issue is while i have a good idea of what Illusion powers are good and what they do I havnt the foggiest on Dark.
IS there a brief guide on what Dark powers i should be getting, which are skippable ect?