Introduction:
I have over 1 000 victories on Mystic, currently at 1 800 MMR. I don't claim I am the best Mystic, nor I claim this guide is perfect. Mystic is a versatile class with multiple ways to play it. It fits into any comp and is playable against any comp. Below I will go through the general build I play and its variations. I will also cover its weaknesses and strengths. In addition, I will mention a few handy tips for different situations. 

My general build: This build has defensive tools against all comps and offers ways to play aggressively. 

Healing vision: Decent bursty heal, use it when you don’t have any CDs available, and your team is under pressure. Try to avoid overusing this ability, it will make you run out of mana faster than the enemy healer, it’s not mana efficient. 
TIP: Pay attention if the target, you want to cast Healing vision on, has healing reduction applied to by an enemy. If yes, use Cleanse before to get the 100 % value out of Healing vision. Currently there are 3 classes which can apply healing reduction: Champion, Assassin, Lich.

Temporal Barrier: Your second most mana efficient spell, close behind Blessing of Sun and Moon. It provides a huge shield for 7 seconds and 15 % movement speed bonus. When the shield is depleted, you are refunded 40 % of the mana cost and close enemies are slightly slowed. Use this when you know a lot of dmg is coming towards your target. Be careful to not use it too early, good opponents will just switch targets. Do not overlook the movement speed bonus and slow, it’s useful for putting some distance between you, or the target you are using it on, and melee enemies. 

Blessing Of Sun and Moon: Your most mana efficient spell and a spell which, in my opinion, separates the best Mystics from the good ones. With 4 seconds cooldown and 8 seconds duration, you can have nearly 100 % uptime on two targets. Always have it on the ally who is being targeted. With its low mana cost you don’t have to be afraid of running out of mana due to using this spell. 

Blackout: AoE fear for 2 seconds. This ability is fantastic for setting up kills but to do so, you must run into melee range. While doing so, be sure you have some defensive spells available to immediately help yourself, such as Temporal barrier, if the aggressive attempt doesn’t work out. 

Spirit Form: 60 second cooldown. When used, it cleanses all debuffs from the target, silences them and makes the invisible. The invisibility lasts for 2,5 second unless cancelled earlier by casting spells. Allies around the target are healed every second, and when the invisibility is broken. 
TIPS: With such a long cooldown, be sure the situation truly deserves using this ability. If used on yourself, you can try to group up with your allies to provide them with the AoE healing, if necessary. Use it to counter big DoTs such as Lingering Demise. Because the initial cast silences the target, be careful not to interrupt your allies’ important spells. Timing is key. 

These abilities, in my eyes, are mandatory in every build and every way you want to play Mystic. For the last 3 spots I usually use: 

Aegis: For 7 seconds you get 30 % damage reduction and are immune to a first Hard Disable ability (Fear, Stun, Incapacitate, Polymorph, Banish). The damage reduction disappears if it prevents Hard Disable ability! Be careful what you want out if this ability. Some great examples of use: Use it on ally Wizard when they are about to cast Meteor to ensure they don’t get CCed. Use it on ally Champion to help him stick to his target. If you are playing against a team which has many DoTs, thus constant damage, and pressure, don’t be afraid to use this spell every time it’s available. 
Cleanse: The best cleanse ability in this game, removing 3 debuffs from an ally target at once and slightly healing them for every debuff cleansed. Before the match, try to think of key abilities which might be worth looking out for to cleanse. Example: Wizard’s polymorph, Champion’s and Assassin’s stuns. Quickly cleansing these effects from your ally can be crucial. If the enemy team doesn’t have abilities such as those, feel free to use Cleanse everytime it’s available to cleanse slows and DoTs. 
TIP: If you are playing against Champion, Assassin or Lich, be sure you use Cleanse before casting Healing vision to get rid of possible healing reduction applied by an enemy.

Astral Shock: One of the two offensive spells I use. Astral Shock has two basic uses: To interrupt important cast from an enemy, or to add pressure on an enemy your DPS allies are focusing due to the increased damage taken part of spell. Like with Cleanse, try to think before the match which enemy abilities are important to interrupt. For example, Wizard’s Polymorph and Meteor or a big healing ability. TIP: When your allies are hard committing to kill one target, save Astral Shock to interrupt enemy healer’s channelled heal. Those abilities usually offer a lot of hp and interrupting them increases your team’s chance to kill the target. It also deals decent amount of dmg, so if you are in a situation where you know you won’t need to interrupt any casts, feel free to use it on enemies to add pressure. 

Sometimes I exchange some of those spells for these spells: 
Dream of Prosperity: In theory a great spell against enemy comp with a constant pressure due to DoTs. Unfortunately, as of now, the spell doesn’t bounce properly making him, in my eyes, not a great choice. 

Disenchant: Sometimes I alternate between Cleanse and Disenchant, depending what comps I play against the most. Disenchant is great for cancelling Wizard’s Crystallize, and Paladin’s/Scholar’s Immortality. The spell has huge value against Elder, to remove his stacks of Mending Spirit, Elder’s most efficient source of healing, or against Lich + Nihil to remove 1 DoT from multiple allies and 1 buff from multiple. 
TIP: unless you are waiting to cancel Immortality/ Crystallize or a specific spell, try to use it as much as possible when multiple players are clumped together. 

Divination: This spell helps you win the mana battle against the enemy healer. Use it with Temporal Barrier against burst, or Healing vision, if your Barrier is not available. Use it with Blessing Of Sun and Moon against constant but low dmg. Use Divination on cooldown to gain as much mana as possible. 

General tips: 
Astral Shock and Blackout are great offensive tools, but they also require you to position aggressively, therefore enemies can attack you much easier. Experienced opponents will use this to kill you. Be very carefully with your positioning.

Focus on keeping up Blessing of Sun and Moon on at least one ally. It should be your top healing spell almost every game. 

Speaking of overall healing, don’t mind the post-game screen or enemy healer’s healing. Mystic’s power comes from preventing dmg, not healing it. 
Mystic has a lot of defensive tools but overall is very squishy. Cycle your defensive tools efficiently to not become an easy target. Use any obstacles, such as pillars, to position correctly and make it as hard as possible for the enemy to attack you. 

Majority of Mystic spells are instant casts. That leaves you with a lot of time between casts. Press that space bar and auto attack! As often as possible.

When facing DPS Paladins, they have a spell, 7 seconds cooldown, which removes the most recently applied buff from their target. Be very mindful in which order  you use defensive spells on the Paladin’s target. Preferably always have Blessing of the Sun and Moon as the most recently applied buff on the Paladin’s target, as it has the lowest cooldown. 

If playing Disenchant and you are facing Wizard who plays Chilling armor, or facing a Lich who plays Underworld Armor, casting Disenchant on them will remove these buffs. If the enemy doesn’t notice this, they will run out of mana much sooner than what would they expect. 

Stat priority
Not useful: Lifesteal, Item Rarity, Reduction of Mana burns. These stats are straight up bad for combat, avoid them. 
Decent: Critical chance, flat HP, flat mana. While not the most efficient or suited for Mystic, they are fine. 
Note: A lot of Mystic’s power comes from shields and applying damage reduction. Neither of them can crit. That’s why Critical chance is kind of bad.  
The best: Mana regen, HP regen, Damage reduction while CCed, Armor, Magic Resist
Note: mana regen is super good, get as much as you can. Stacking Damage reduction might become mandatory if you keep facing double melees, to avoid dying in CC chain. 

Main stats
1 Intelligence gives 7,92 Power 1 mana, 1 Magic Resist and 0,004 % crit chance.
1 Wisdom gives 6,69 Power, 2 mana and 0,02 mana regen per sec
Personally, I think the stats are so close in terms of value that it doesn’t matter.  For biggest Power gain (increasing your damage and heals) go Intelligence.






Popuuuh's Standard Mystic build

My general build I play and its variations. Mystic's strengths and weaknesses. 

TCC MYSTIC

A build you can start with. Use your offensive potential wich leads to less dmg for your team. Skills to consider: -disenchanting -divination -mana burn (for hybrid builds)

Build of Kings

Mystic

Top Mystic Builds

All Mystic Builds

Top Mystic Builds

Popuuuh's Standard Mystic build

TCC MYSTIC

Good all around Build

All Mystic Builds

Popuuuh's Standard Mystic build

TCC MYSTIC

Good all around Build