We've got a big Demo Update here including a brand new system revolving around Ascension classes. Quite a few things have changed regarding the Ascensions so here goes... Combat Arts now grant Ascension XP each time they're used. You can see in the details which Ascension a combat art contributes XP to for a given Origin. Upgrading a Combat Art during a run will also increase the amount of Ascension XP it earns.
When you've earned enough XP you can trigger your Ascension at any time. You can see your progress toward Ascension with the Ascension XP tracker below the hotbar during a run or from the Destiny screen. This replaces the system where you would always select your Ascension after the second stage and allows for flexibility on when you ascend based on your build strategy.
Pact System
Choosing an Ascension unlocks access to 3 Pact Slots in the Destiny screen: Blood, Fortune, and Destiny.
Each Pact type carries a different cost: Blood costs 50% Max HP, Fortune costs 25% of current Gold, and Destiny costs 3 Destiny Points.
Ascensions start at Codex Rank I with 1 Pact Slot, you can choose which Pact slot you want to fill from the Destiny screen during a run: Blood, Fortune, or Destiny.
A second slot opens at Rank V and the third at Rank X by ranking up at the Codex.
Each Ascension has access to 9 Pacts across the 3 categories, ranging from permanent auras and damage type conversion to status chain reactions and Slays (insta-kills) on dodge or block.
There are currently 40+ Pacts in the Demo but more are to come in the full release.
Outlander
Skirmisher Ascension Pacts
Dagger Storm: A permanent aura that throws daggers at all nearby enemies.
Rupture: Hemorrhaging enemies rupture upon death.
Marauder's Reflex: Chance to reset an evade charge any time you Slay an enemy.
Deadly Riposte: Slay an enemy when you dodge their attack.
Venomous Veins: Causes the Poison status effect to puddle every tick on bleeding enemies.
Toxic Seepage: Bloody diseased pulse wave every tick.
Martial Expertise: Chance to reset the cooldown of a Martial Weapon Technique any time you critically hit.
Dagger Trap: When any destructible is destroyed a trap is sprung, damaging nearby enemies.
Grace of the Ancients: Resurrect once with 20% max health.
Arcane Trickster Ascension Pacts
Trickster's Gambit: A permanent aura that throws energy cards at all nearby enemies.
Tithings: Charmed enemies have a chance to drop gold each tick.
Sacrificial Lamb: Charmed enemies explode when they die.
Blood Lightning: Electrified and Bleeding enemies have a chance to emit a bolt of lightning that targets a random enemy each tick.
Arcane Infusion: Increases Starbound proc chance and adds a random arcane damage type to all Starbound bolts.
Winter's Ember: Causes a blast of blue flame when an enemy is both Burning and Freezing.
Fated Catalyst: On every Lucky Roll selected, temporarily increase all arcane damage types by 100%.
Charismatic: Enemies have a chance to become Charmed.
Grace of the Ancients: Resurrect once with 20% max health.
Soldier
Warrior Ascension Pacts 
Executioner's Reach: Chance to Slay enemies hit within point-blank range.
Blade Storm: A permanent aura of whirling blades.
Spiked Armor: When damaged, deal Physical damage and cause Bleed to the attacker.
Deadly Rebuttal: Slay an enemy when you block their attack.
Colossal Arsenal: The base size of all Martial Technique skills is increased.
Swift Retribution: Striking down a projectile has a chance to Slay the attacker.
Ranged Expertise: Chance to reset the cooldown of a Ranged Weapon Technique any time you critically hit.
Vanquisher's Favor: Temporarily increases the max projectiles of all skills whenever an elite is killed.
Grace of the Ancients: Resurrect once with 20% max health.
Death Knight Ascension Pacts 
Avatar of Death: Embody the Avatar of Death. All attackers are immediately struck by retaliatory death damage with 100% status chance.
Combustive Corpses: A permanent pulsing aura that causes nearby corpses to explode with Death damage.
Focused Malice: All damage from every skill is converted into Death damage. All Death damage is increased.
Reanimation: When an enemy with Electrified and Corrupted dies they are reanimated and fight for you.
Icebone Dreadnought: When slain, Freezing and Corrupted foes have a chance to merge with surrounding corpses to rise as a frozen behemoth.
Vampiric Reckoning: Bleeding and Corrupted enemies have a chance to lifetap each Bleeding tick, in addition to the existing Corrupted lifetap chance.
Unholy Frenzy: Your summons have their movement and attack speed increased by 100%.
Hellfire's Embrace: Chance to reset cooldown on a Incendiary Sorcery any time you critically hit.
Grace of the Ancients: Resurrect once with 20% max health.
Astrologer
Astromancer Ascension Pacts
Avatar of the Stars: Embody the Avatar of the Stars. All attackers are immediately struck by retaliatory astral damage with 100% status chance.
Celestial Aura: A permanent aura of protecting stars.
Starbound Orb: Starbound enemies have a chance to create a damaging orb with each tick.
Overcharged Bolt: Starbound enemies have a greater chance to proc the Starbound Bolt. Also the bolt size is increased, damaging more enemies.
Astral Embers: Adds fire damage to Starbound bolts on enemies that are both Starbound and Burning.
Corrupted Wisp: Upon death Starbound and Corrupted enemies have a chance to summon an aggressive ricocheting wisp.
Deep Insights: Knowledge temporarily increased any time an elite enemy is killed.
Lucky Stars: Every time you critically hit, chance to temporarily increase Luck.
Grace of the Ancients: Resurrect once with 20% max health.
Elementalist Ascension Pacts 
Avatar of Fire: Embody the Avatar of Fire. All attackers are immediately struck by retaliatory fire damage with 100% status chance.
Avatar of Earth: Embody the Avatar of Earth. All attackers are immediately struck by retaliatory physical damage with 100% status chance.
Avatar of Ice: Embody the Avatar of Ice. All attackers are immediately struck by retaliatory ice damage with 100% status chance.
Flashpoint: Burning effect has a chance to trigger an additional burst of fire.
Winds of Winter: Temporarily boosts Freezing spread when an elite enemy is killed.
Frost Fire: Freezing and Burning enemies have a chance to pulse a burst of Ice and Fire each tick.
Circle of Elements: A permanent aura that creates a protective elemental orb.
Wildfire: Temporarily boosts Burning spread when an elite enemy is killed.
Grace of the Ancients: Resurrect once with 20% max health.
Ascension Weapon Evolutions
When choosing your Ascension, alongside the various stat buffs gained, you will also see that your starting Skill evolves depending on the Ascension you choose.
Outlander
Skirmisher Weapon Evolution
Barbed Shot: Chance to cause Hemorrhage to Bleeding enemies. 
Arcane Trickster Weapon Evolution
Prismatic Shot: A random Elemental damage type is applied to each shot fired.
Soldier
Warrior Weapon Evolution
Defensive Slam: Every Critical Hit has a chance to increase Block chance.
Death Knight Weapon Evolution
Corrupting Slam: Chance to create explosive burst of deathly energy on hit.
Astrologer
Astromancer Weapon Evolution
Overcharged Missile: Increases missile size and bonus projectile count. 
Elementalist Weapon Evolution
Primal Missile: Assigns a random Elemental Damage Type to each missile fired.
Bugs and Quality of Life
Fixed burning enemies showing through Void Breach.
Added Teleport animation to character after selecting stage door.
General tweaks to overall game speed.
Increased friendly fire damage inflicted by Flying Jesters.
Maybe bosses less likely to teleport during their battles.
Increased damaged caused by destructible for enemies.
General UI art polish throughout.
Made minor changes to early gear drop chances, so that it's more likely to get a full set of tattered earlier.
Auto Aim now prioritizes bosses if there is one nearby.
Lock Box now stores Rune Fragments and Reroll Cubes even on an unsuccessful run.