
The Investor
At start of combat, spend 4 Shards to give Gustav an Investment. Give all Heroes 2 Mana Regen per Investment. Backup.
Every 5 Investments, gain 30 Shards.
The Analyst
“I've been wanting to test a scenario like this.”
A 150 Max Mana Mystic whose Blizzard deals damage and Mana Regen-scaling Frost to enemies and gives allies Magic-scaling Shields. The Investor is a Backup that turns Shards into Mana Regen for everyone, The Glacier is a defensive pick that keeps Blizzard on itself, and The Avalanche grows with Shards. Pairs with Grace's The Radiant.

Create a Blizzard for 5 seconds.
Each second, inflict 2 (+1 per 8 Mana Regen) Frost and deal 15 (+50% Magic) damage to enemies inside the Blizzard. Shield Heroes inside it for 10 (+75% Magic).
At B rank you pick one of three. Tap the cards to compare.

At start of combat, spend 4 Shards to give Gustav an Investment. Give all Heroes 2 Mana Regen per Investment. Backup.
Every 5 Investments, gain 30 Shards.

Gains class Tank
Blizzard applies (+75% Defense) more Shields and always targets Gustav.
After Stall (25 and 50), permanently gain 2 (+2 per rank) Defense.

On cast, gain 1 Shard.
On Shards generated, gain 1 Mana Regen and 5 Magic.
Specializations, upgrades and items players picked for Gustav in shared builds. Each shows the pick rate (bold), the clear rate of builds with that pick, and the number of builds.
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Picked from the game data to match Gustav's mechanics, class and the stats their abilities scale with. The tags before each item name say why.

+4 Mana Regen+25 Magic
If this item is held by a Mystic, double its stats.

+25 Starting Mana+4 Mana Regen+25 Magic
On cast, remove 30 Frost from each enemy with 30 or more Frost to Stun those enemies for 2.5 seconds.

+25 Starting Mana+4 Mana Regen+25 Magic
Whenever the holder Shields another Hero, damage all enemies equal to 50% of the Shield applied.

+4 Mana Regen+25 Magic
On cast, inflict 12 Frost on the nearest enemy.

+25 Starting Mana+4 Mana Regen
Every 4 casts, if held by a Mystic this item gains 1 Mana Regen.

+4 Mana Regen+20 Attack Speed
If this item is held by a Mystic, double its stats.
A and S rank upgrades are class upgrades: the options come from the hero's class, not the hero (game tutorial). In the current data the A and S rank options are the same list. S rank heroes also get one more item slot. Expand to see the options.

Mystics gain 1 Mana Regen for each reroll this game. Backup.

Every other cast, gain 3 Shards.

Backup Only: At start of combat, gain 5 Shards and give Heroes 500 (+500 per rank) Shields.

On Stall trigger, gain 1 Shard and give Heroes 3 Mana Regen. Backup.

After Stall (30), permanently gain 5 Mana Regen.

Stall abilities trigger 6 seconds faster. Backup.

When this Hero applies Shields, apply 50% more Shields.

On cast, give other Heroes (+100% Mana Regen) Attack and (+100% Mana Regen) Magic.

At start of combat, give this Hero and adjacent Heroes 400 (+250% Magic) (+1000% Mana Regen) Shields.

Backup Only: At start of combat, give Heroes 4 (+4 per rank) Mana Regen, 50 (+25 per rank) Attack, and 50 (+25 per rank) Magic.

On cast, give the lowest percent health Hero 100 (+500% Mana Regen) Shields.

On cast, permanently gain 4 Magic.

On cast, increase the amount of each Debuff on enemies in range by (+50% Mana Regen).

On cast, gain 1 Mana Regen for each type of Debuff on all enemies.

On cast, give the lowest percent health Hero 1 Shield per 2 Debuffs on all enemies.
How to read the numbers: base value (+N% Stat) adds N% of that stat, (+A per B Stat) adds A for every B of that stat, and values split by slashes (/) are per rank.