Faerie Dragon (Warcraft III)

Small, quick flying unit, effective against enemy casters. Though not actual Dragons, these mystical looking creatures police the Emerald Dream from magic. As such, they are immune to magic. Attacks land and air units.

Information
The Faerie Dragon is an anti-spellcaster unit that also doubles as both a ground and air attacking unit. Generally in such cases, Hippogryph Riders would fulfill the role of ground and air attackers better due to their higher health and rate of fire.

Mana Flare is their best spell and should always be in use when numerous spellcasters are used by the enemy. While the Faerie Dragon cannot attack in this state, any spells cast in its range prompts the Faerie Dragon to blast them with a bolt of magic which possesses AoE capabilities, and it also has an additional 12 armor while in this state. Though it can only affect a single unit every 12 seconds, numerous spellcasters mean that Mana Flare will continually go off and kill groups of spellcasters with ease.

Faerie Dragons are also spell immune, protecting them from Gryphon Riders and Frost Wyrms, who would otherwise kill them extremely fast. This doesn't keep them safe from other units however, who can easily focus them down even through the increased armor given from Mana Flare.

Phas Shift (Autocast)

 * Causes this unit to shift out of existence whenever it takes damage. While out of existence, this creature cannot: attack, move, cast spells, be attacked, or have spells cast upon it.

This spell is automatic by default. Keep it so that the Faerie Dragon won't get mowed down easily by anti-air units.

Mana lare

 * Causes the Faerie Dragon to channel negative magical energies that damage nearby enemies when they cast spells.
 * Also increases the Faerie Dragon's armor by 12.

The damage is 3 per mana point the unit currently has, up to a maximum of 90, or 1/mana point with a max of 50 (before spell damage reduction) for heroes. The damage has a splash radius of 20 that only affects spellcasters. A given unit can only be hit every 12 seconds by the faerie dragon casting this spell.

Have your anti-air units focus on any Faerie Dragons using Mana Flare to kill them off and protect your spellcasters.
 * Counters