Hello, I am GameOveRus and I welcome you to my Taric guide.
This is a AP Nuke\Support Taric (Maybe even tank, if it goes REALLY well)
It helps your team by a huge amount, but also doesn't leave you completely nothing without a team.

Magic Pen Marks: for extra damage with our spells.
Mana Regen \5 per level Seals: Taric's mana costs are huge, so that helps us bit.
Cooldown Reduction Glyphs: makes spamming a bit easier, especially if you last hit minions a lot.
Ability Power Quintessances: Raw Imbue and Dazzle AP-ratios early game.

9-0-21
Standard AP-carry mastery set.
Also viable:
0-9-21
A bit of a tanky support - take Strength of Spirit, not Nimbleness or any dodge masteries.
0-21-9
Full tank with a little bit of support.

Rod of Ages, Rylai's Crystal Scepter and Abyssal Scepter - gives us the survivability, not forgetting about our burst damage and AP-nuking abilities.
Nashor's Tooth for even more burst, and trying to make the best out of Taric's Passive, replenishing mana with attacks.
Rabadon - just AP. Even more nuke, even more damage.

Maxing out Dazzle first gives us some damage coming with a stun for an enemy.
Taking Imbue next doesn't let our teammates die.
Shatter last for increasing our AD-carries damage (can take after Dazzle, if enemy team starts building armor, and your AD-teammates are having a hard time)
Radiance when can - use it when your team is pushing a tower, or in the middle of enemy team.

Ghost and Flash:
Awfully good summoner spells, making us almost uncatchable.
Also can take:
Clarity - mana spikes early game.
Clairvoyance - a nice support spell, rarely taken.
Rally - synergize with our Ultimate, helps pushing.
Ignite - if you want kills early game for better equipment.

Ok, that's it.
Credits go to:
Me, the mighty GameOveRus (Ego OVER 9000)
All my friends - I love ya all :D
Thank you!
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"More than just precious stones - I bring new and ancient power" (c) Taric