This information has been released by Ubi/Nival about H5 addon 2: "Tribes of the East". It is still a work in progress, and anything might change until release.
SabotageNEW in ToE: can paralyze any mechanical unit on the battlefield (golems, ballista, catapult, tents, town towers) for one turn, if the target's total hit points are lower than the gremlins'.Gremlin Saboteur
Elemental AuraNEW in ToE: all creatures (including allies) standing near the Marble Gargoyles become vulnerable to elemental magic.Marble Gargoyle
Elemental VulnerabilityNEW in ToE: any creature vulnerable to elemental magic receives 50% more damage from fire, air and water based spells.Marble Gargoyle
Obsidian SphereNEW in ToE: Obsidian Golems are immune to all non-damaging spells. Direct damage spell, instead of dealing magical damage, heals and resurrects the Golems. The amount of restored hitpoints is equal to 50% of the normal spell damage.Obsidian Golem
Destructive Magic MagnetismNEW in ToE: If the Golems suffer from a destructive area spell together with allied units, they can absorb a portion of the damage to themselves.Obsidian Golem
Eldritch AuraNEW in ToE: effect unknown yet.Battle Mage
Luck GamblerNEW in ToE: Viziers can increase the luck of a friendly creature or decrease the luck of an enemy creature, three times per battle but only one time per target. The duration of the effect is equal to the Viziers Spellpower.Djinn Vizier
WhirlwindNEW in ToE: can break through six tiles in front of them (??).Rakshasa Kshatri
Call StormNEW in ToE: Storm Lords can summon 3x3 tile sized cloud to any place on the battlefield. Every creature that gets under the cloud receives 10 points of damage for each colossus that summoned the cloud. Shooters under the cloud receive 1% penalty to ranged attack for each Storm Lord.Storm Lord
Ability Lvl 1 (Goblins)NEW in ToE: Goblins Shamans have the ability to disrupt spells from an enemy hero or casting unit. If the goblins fail, the spell they were trying to disrupt will be cast on themselves. Goblins Hunters can set traps, which are invisible to the enemy.
Ability Lvl 2 (Centaurs)NEW in ToE: Centaurs are the fastest shooters in the game, but take four tiles on the battlefield. Centaurs Nomads can run away from the enemy, after being hit and then retaliate by shooting with half their normal strength. Centaurs Marauders have no melee penalty.
Ability Lvl 3 (Orc Warrior)NEW in ToE: One of the upgrades of the Orc warrior can take hits, which were targeted on a nearby friendly stack. His retaliation is 1.5 times stronger than normal attack.
Ability Lvl 4 (Shamans)NEW in ToE: Shamans, Human and succubus hybrids, can cast Haste and Slow. One of the upgrades, when engaged in melee combat will curse the opponent (Slow, Suffering, Weakness, Vulnerability).
Ability Lvl 5 (Orc Warlords)NEW in ToE: Orc Warlords raise the initiative of all friendly creatures by one.
Ability Lvl 6 (Pao-Kai)NEW in ToE: Pao-Kai is one of the upgrades of the Wyvern. It is immune to blind, because it has no eyesight to begin with. Its electric discharge attack harms everyone standing near the target (the amount of damage is divided among those affected by the discharge). In addition, the Pao-Kai can eat dead bodies to restore its health.
Ability Lvl 7 (Cyclops)NEW in ToE: Cyclops is a strong melee fighter, with the ability to attack walls, when in siege battle. One of the upgrades of the Cyclops can shoot a beam from his eye that affects several creatures, and decreases his victims luck.
InvisibilityNEW in ToE: Stalker and Shadow Mistress can turn invisible for the enemy until it attacks or is adjacent to an enemy unit. The ability works only once per battle and lasts for three rounds. Shadow Mistress can cast spells without being exposed.Stalker, Shadow Mistress
Immunity to CurseNEW in ToE: immune to the Weakness spell?? other curses??Blood Witch
Aura of BraveryNEW in ToE: all (allied?) nearby (3 tiles radius) creatures have positive Morale (at least +1).Minotaur captain
Ride-by-AttackNEW in ToE: The Black Rider, when attacking a distant target, deal 25% of his normal damage to any enemy standing adjacent to his path, without retaliation.Black Rider
Acid BloodNEW in ToE: When the Acidic Hydra takes damage, it spills acidic blood 4 tiles in the direction of the attack. The acid damage is equal to 25% of normal damage dealt by the stack of Hydras.Acidic Hydra
IncinerateNEW in ToE: The Red Dragon can attack an adjacent enemy with a powerful blow, dealing 50% more damage, and without receiving retaliation.Red Dragon
Hold GroundNEW in ToE: unknown yet (unless this is inverted with "Prepare Position").Stone Defender
Prepare PositionNEW in ToE: As long as Defenders do not move, their receive a +5 bonus to Defense.Stone Defender
Harpoon StrikeNEW in ToE: Harpooners can shoot harpoons that in addition to standard damage can pull the target one tile closer to the Harpooner.Harpooner
Bear RoarNEW in ToE: When Bears attack, they can frighten the target and enemy creatures that stand nearby. The Bear receives +1 to his morale and +10% to his health. The effect lasts for two turns.White Bear Rider
Battle RageNEW in ToE: Every time the Battlerager receives damage, he gets a +2 bonus to initiative and +5 bonus to attack, for two turns.Battlerager
Anti-GiantNEW in ToE: When fighting against large creatures, the Battlerager receives a +4 bonus to attack and defense.Battlerager
Avenging FlameNEW in ToE: After death, the Flame Keepers' inner flame escapes and deals fire damage to every enemy in the surrounding tiles. Level of damage depends on the amount of Flame Keepers in the dead stack at the start of combat.Rune Keeper
Flame WaveNEW in ToE: Once per battle, Thunder Thanes can do 1.2 times standard damage to any creature (?).Thunder Thane
FlamestrikeNEW in ToE: the creature can place "Mark of fire" on its targets (?).Thunder Thane
Flame BreathNEW in ToE: When the Dragons attack, they leave a fire wall for 2 turns, that deals 10 point of damage for each Dragon in the stack.Lava Dragon
Siphon ManaNEW in ToE: steals mana from enemy hero and distributes it evenly between all casters in the creature's army.Quasit
LeapNEW in ToE: the creature can attack a target by jumping towards it, over any obstacles, provided there is a free spot near the target. The damage dealt by the attack increases with the distance of the jump (10% per tile).Horned Leaper
Immune to Puppet MasterNEW in ToE: this creature cannot be hypnotized by the Puppet Master spell.Succubus Temptress
SeduceNEW in ToE: one time per battle, the creature can seduce an enemy stack, making it fight for its own army. (Can the effect be dispelled?))Succubus Temptress
Searing AuraNEW in ToE: any enemy adjacent to the creature at the start of its turn will suffer 10*Hellmare_Stack_Size of fire damage..Hellmare
Axe of SlaughterNEW in ToE: damage inflicted by the creature is increased by 2 for each creature in the target stack.Pit Spawn
Summon OtherNEW in ToE: the creature can teleport any stack on the battlefield, in the radius of its movement area, to itself in a straight line.Arch Demon
Magic-proof 25%NEW in ToE: Attacking spells inflict 25% less damage to this creature??Skeleton Warrior
Weakening AuraNEW in ToE: all nearby (adjacent?) non-undead creatures suffer -2 to Attack and Defense and -1 to MoraleDisease Zombie
Ammo StealNEW in ToE: the creature can steal ammunition from a chosen shooter in its movement range. The amount of removed ammunition is equal to the creature's weekly growth.Poltergeist
Sleeping StrikeNEW in ToE: the target has a chance to be put to sleep for 3 turns (i.e. ATB value frozen?).Nosferatu
Death WailNEW in ToE: the Morale of all the enemy creatures is decreased by 1.Banshee
Sorrow StrikeNEW in ToE: cast sorrow on attack with basic mastery (decrease Morale?/Luck? of the target).Horror Dragon
Treant UnionNEW in ToE: Once per battle, Dryads will be able to heal and resurrect Treants (4 Hit Points per Dryad), and be healed at the same time (20 Hit Points per Treant).Dryad
AgilityNEW in ToE: Bladesingers gain +2 Defense for the next turn per every tile walked.Blade Singer
Force ArrowNEW in ToE: Sharpshooters ignore 75% of target's defense, and his shoot can throw the target back by one tile.Sharp Shooter
Power FeedNEW in ToE: High Druids can transfer their magical power to the hero, increasing his Spellpower. The effect lasts until there are no more druids alive.High Druid
Bond of LightNEW in ToE: Any non-damaging Light Magic spell cast in combat is also cast on the White Unicorns, regardless of the caster.White Unicorn
Rage of the ForestNEW in ToE: Anger Treant's ability "Rage of the Forest" can be activated only once per battle, and lasts until the end of the battle. Treants will transfer half of their defense to attack, increase their initative by 2 and loose the ability to entangle enemy.Anger Treant
Rainbow BreathNEW in ToE: Rainbow Dragon's fire attack can affect one to five tiles, depending on luck.Rainbow Dragon

Thanks to sfidanza for the work on this page.
Thanks to ThE_HyDrA for creating and looking after the Heroes 5 section of Age of Heroes!