Traits

Traits are secondary modifiers of in-game mechanics. They're divided in two main categories: unlockable traits and ascension perks.

Pre-Unlocked traits
When you start a new game you're given the choice to choose a maximum of 2 traits which have both positive and negative effects.

Prepared
This trait is most useful on high Curiosity builds (works on rank 7 Insignt and Karma bonuses too), especially if Purple Smart is chosen as adviser as it gets 100 Bits from her passive.
 * +50% starting resources
 * 1x Free Town Square
 * 10% more Love Magic to rank up
 * Pre-unlocked

Environmentalist
This trait increases/decreases Happines per day by 4 per Eco Score above or below 12, up to +64 and with diminished ratio if the population is < 100. Works pretty well with high Karma builds and if Timid Yellow is chosen as adviser as she passively provides a +3 Eco Score bonus and she also may permanently convert Gardens to Trees using her Regenerate power.
 * Bonus Happiness when Eco Score is > 12
 * Malus Happiness when Eco Score is < 12
 * Pre-unlocked

Scientist
This trait is the most neutral since Tech Points and Love Magic are easy enough to generate both with and without these modifiers.
 * +40% Tech Generation
 * -10% Love Magic Generation
 * Pre-unlocked

Harmonious
This trait grants 0.2 Happiness per day per Defense Rating, up to +64 with diminished effect if population is < 100.
 * Bonus Happiness for Defense Rating
 * -50% Raid Effectiveness
 * Pre-unlocked

Botanist
This trait is best when the strategy focuses on rushing Love Magic generation while building no Quarry (Gems may be bought in the Town Square, converted from Bits in the Factory, produced by Stores using the Rock Candy Ascension Perk or converted from Tech and Prisms in the Alchemist Lab).
 * +1 Garden Radius
 * +10% Love Magic generation from Houses in the Garden's Radius
 * +1 Quarry Radius
 * Pre-unlocked

Investor
This trait is best with high Curiosity builds (benefitting a lot also from the Rank 10 Charisma), and/or when using Apple Horse advisor, when stacking skill points on Tradecraft, and keeping a Town Square in economic growth mode (especially having at least the 7th Rank in Charisma). Trading prices of Gems and Prisms periodically change, making it possible to earn Bits by buying when they're cheap and selling when they're expensive. The reduced price variation rate shouldn't actually considered as a drawback since a trader build would focus on selling Food while prices for Gems and Prisms are bad, and if they're not a good Trader'd have more time to perform his haggle.
 * +3 Max Traders
 * +100% Trading Quantities
 * -80% Trade Price Variation Rate
 * Pre-unlocked

Cheapskate
This trait is the most worthless. The building cost reduction affects only the Bits required during the building process, while Gems/Prisms/Obsidian and the Upgrade costs are unaffected; not to mention that the drawback forces the player to skybuild, or buying new Tiles for residential purposes, or even resorting to unefficiently spend gems on Villae in order to reach Ascension.
 * -10% Building Cost
 * -2 Housing Slots for Houses
 * Pre-unlocked

Hedonist
This trait becomes useless in the 9-11th ascension as skills won't progress above level 10 and not every single one of them is relevant.
 * +100% Love Magic Generation
 * -50% Bits earned from houses
 * Pre-unlocked

Mercantile
This trait is best in high Curiosity builds (benefit also from rank 10 Charisma), and/or when using Apple Horse advisor, when stacking skill points on Tradecraft, and keeping a Town Square in economic growth mode (especially having at least the 7th Rank in Charisma). Cutting off Libraries and Quarries as sources of income, one can supply by trading Gems and Prisms at the Town Square, buying those when they're cheap and selling them when they're expensive.
 * +400% Trader Rate
 * +8 Happiness per day
 * Only Houses generate Bits
 * Pre-unlocked

It also synergies amazingly with Venetian, if you're man enough to pick that.

Prospector
Induces the player to build many quarries in residential area to benefit from their bonuses, until one eventually notices the Eco Score dropped severely and there's no way to restore it by counter-gardening.
 * Quarries don't disturb residents
 * Gardens don't improve Eco Score
 * Pre-unlocked

Socialist
Quarries cost 420 Bits, Factories cost 720 Bits. While the formers are not necessary to the game, the latters are still needed to unlock Tier3 structures to get the first Ascension.
 * Town Squares radius is increased
 * +20% Quarry and Factory cost
 * Pre-unlocked

Carefree

 * +30 Maximum Happiness
 * Cannot use Edicts
 * Pre-unlocked

Equality
This trait is currently pre-unlocked and its real great drawback are the fixed stats. Assigning the points manually allows the player to get all ranks 5, saving 2 extra stat points. Selecting this trait won't trigger any rank 7/10 bonuses of the Specialized ascension perk.
 * Every Stat becomes rank 5
 * Happiness is always 50
 * Pre-Unlocked

Unlockable traits
These traits require to be unlocked by achieving certain conditions in game.

Alcoholic - pending for confirmation
This trait is unlocked by building 3 Taverns in a single game. This trait boosts greatly the speed of the first ascension, allowing an immediate access to tier 2 buildings once the Tavern is finished, also the increased range nearly affects the whole starting map.
 * 1x free Tavern
 * Tavern radius is increased
 * +30% Effect of Taverns
 * Taverns are the only source of Happiness

Capitalist

 * Stores generate Bits
 * -25% Tax Penalties
 * Unupgraded Houses reduce Happiness
 * Unlocked when Bits per day Income > 500

Cursed
Naturally-spawned Trees become gloomy and passively grant Mana per day. This trait is most efficient with high Karma builds, and choosing Timid Yellow who cannot only permanently convert Gardens to Trees due to its Regenerate power, but also earn Gems based on the Eco Score provided by adviser-spawned trees. Any Tree destroyed, even for building tree houses, will anger the god causing several unpleasant drawbacks like a severe drop of Happiness. Buying new tiles will increase the number of Trees on the map, causing the mana to grow even faster.
 * +0.3 Mana per day per Tree
 * Destroying Trees angers the God
 * Unlocked by building over several Trees in a single game

Empyrean

 * +3 Town Squares radius
 * -50% Town Squares cost
 * Town Squares can only be built in sky tiles
 * Unlocked at Tavern for 750 Tokens

Explorer

 * Scouting Specialists occasionally grant free Tiles
 * -50% Scouting Efficiency

Heroic

 * +1 Specialist
 * Double neutral encounters
 * Ignored Neutrals become aggressive
 * Unlocked by building 4 Armories and 4 Keeps

Skycrafter - pending for confirmation

 * -50% Cloud Cottage Cost
 * +300% House Cost

Genghis Pony - pending for confirmation

 * +1 Starting Specialist
 * +100% Raid Frequency
 * +100% Invasion Frequency

Superstitious
The bonus Mana per day is worth only during the first days in game. The regeneration bonus becomes useless in the most-likely scenario you'll have filled the Happiness gauge with a bonus >= 50 Happiness per day.
 * +5 Mana per day
 * +25 Maximum Mana
 * Cannot gain Mana from excess Happiness
 * Unlocked at Tavern for 500 Tokens

Tyrant

 * +100% Edict Potency
 * Edicts last 1 day
 * -50 Maximum Happiness
 * Unlocked by having Diplomacy ranked 5.

Venetian
Gardens and Armouries become useless with it. Gardens still give ecoscore. Armories still let you purchase specialists. I wouldn't say useless, just pointless to make more than one. Also if you get the Botanist trait, it gives gardens enough radius to work with venetian.
 * +50 Maximum Defense Rating
 * Trades grant Happiness
 * -1 All Structures radiuses
 * Unlocked at Tavern for 1500 Tokens

Veteran
Tier 3 Charisma grant an additional Specialist, but only the first one is rank 10. That means it's almost impossible to avoid the drawback.
 * First Specialist starts at rank 10
 * -50% Specialists training speed
 * Unlocked when leveling a specialist up to 10

Well-Fed
Sorry I did not discover this one yet
 * -35% Unhappiness from population
 * Ponies consume twice as much Food

Wizard
It should be noted that Skills are NOT Stats, therefore this trait won't be of any help should one attempt to exceed the rank 10 cap for Stats.
 * +1 to all Skills
 * +100 Maximum Mana
 * Cannot generate Love Magic
 * Unlocked at the Tavern for 6000 Tokens

Ascension Perks
Ascension perks are special traits that have almost no drawbacks, awarded each time one ascends. When ascending there will be a list of 6 possible Ascension Perks to choose one from.

Nomadic
Nomads don't require food or happiness, because they are in a constant state of unhappiness and bring down any citizens that move in, driving them away. Dooming you to 50 Nomads, generating no love. All you can do is sit there and wait for death.
 * +50 Maximum Population
 * Population can never drop below 50

Rock Candy

 * Stores produce Gems when population is > 100
 * Ponies eat Gems and produce Happiness

Blacksmith

 * Armory radius increased
 * +50% Armory Effect

Expansive

 * -25% Cost of new Tiles
 * Bigger starting map

Specialized

 * +100% Effect of Rank 7 Stats
 * +100% Effect of Rank 10 Stats

Engineer

 * Shield Generator radius increased
 * +30% Shield Generation speed

Maximizer

 * +4 Max Population per House
 * -1 Quarry Radius

Mystical

 * Using powers generate gems = (Max Mana/10)

Persuasive
This perk does NOT refresh the amount of trades, but the price rating. This arguably counters the drawback of the Investor trait.
 * Using powers refreshes trade prices
 * +5 Maximum Traders

Demolitionist

 * Full Refund when Demolishing
 * Raiding is more effective

Natural Defense

 * +25% Trees Eco Score
 * +400% Trees Defense Rating

Adamant

 * +50 Defense
 * +50% Defense rating from Armories

Paranoid

 * -20% Aggressive Encounters
 * +50% Scouting effectiveness

Sylvan

 * No Gem cost for Tree House
 * +8 Tree House Capacity
 * No Bits cost for Gardens

Tycoon

 * -10% Structure Costs
 * +100 Bits

Industrious

 * Negative Eco Score grants Happiness
 * +1 Defense per day from Factories

Tranquil

 * +10 Max Happiness
 * Excess happiness also gives Love Magic