Skill Combination Effects

Some heroes' skills can be combined to create an additional effect. (These were all I could remember, I would appreciate assistance with the rest. -siege)

United Creeps

Nightmare + Spire

• Units hit by spire under the effects of nightmare will be frozen for a short amount of time and damaged (broken in 1.12)

Encouragement + Rebirth

• When a unit enchanted by rebirth is sacrificed by encouragement a flying unit is spawned from it's corpse

Nightmare + Howl

• Waking units from a nightmare with howl deals damage and instantly wakes them

Elven Brigade

Flame of the Devout + Dash

• Dashing through the flame leaves a burning trail behind that deals damage to enemies that come into contact with it

Backfire + Syphon Sigil

• Using Syphon on a hero with Backfire on it will cause the Glyph to drain mana and deal damage instantly rather than over a short period

Maelstrom + Incinerate

• Incinerating the tornadoes created by Maelstrom will light them aflame, adding unit damage to the existing building damage effect

Tactician Banner

Soul Binder

• Flaming Orbs - causes the banner to gain an attack

Divine Wizard

• Holy Thunder - deals damage to nearby enemies

Rune Knight

• Dismantling Aura - reduces armor of nearby enemies

Aeromancess

• Concentration Aura - increases mana regeneration of allied unitds

Arcane Archer

• Trueshot Aura - increases ranged damage of allied units

Blazing Priest

• Burning Banner - deals damage to close enemies

Infiltrator

• Trapped Banner - acts like a detonating explosive when detroyed

Time Cleric

• Endurance Aura - increases the speed of allied units

Grim Brigade

Holy Strike + Ki Blitz

• When Divine Wizard casts holy strike on High Oracle while she is channeling ki blitz, the healing orbs have a mini holy strike effect on them as they fly through the air. This appears to be a purely graphical combination, and it is unknown whether this effect was intended.