Druids get a new ability in Mists of Pandaria called Symbiosis. It's the most interesting spell of the whole expansion and the mechanism behind it is very unique.

Here's the tooltip from WoWHead.

To offer a simple explanation: The druid creats a link with another player.The target player is granted ONE druid ability depending on his specialisation(healer would get a healing spell for example).The druid is granted ONE ability depending on the target's CLASS/Spec.

Another example: You are a restoration druid. Your target is a priest. Casting Symbiosis will grant you Leap of Faith. The priest will get Tranquility.

Spells gained by the druid:

Class	Druid specialisation
	Balance	Guardian	Feral	Restoration
Death Knight	Anti-Magic Shell	Bone Shield	Death Coil	Icebound Fortitude
Hunter	Misdirection	Ice Trap	Play Dead	Deterrence
Mage	Mirror Image	Frost Armor	Frost Nova	Ice Block
Monk	Grapple Weapon	Elusive Brew	Clash	Fortifying Brew ?
Paladin	Hammer of Justice	Consecration	Divine Shield	Cleanse ?
Priest	Mass Dispel	Fear Ward	Dispersion	Leap of Faith
Rogue	Cloak of Shadows	Feint	Redirect	Evasion
Shaman	Purge	Lightning Shield	Feral Spirit	Spiritwalker's Grace
Warlock	Unending Resolve	Life Tap	Soul Swap	Demonic Circle: Teleport
Warrior	Intervene	Spell Reflection	Shattering Blow	Intimidating Roar

Class	Specialisation
Death Knight	Blood	Frost & Unholy
	Might of Ursoc	Wild Mushroom: Plague
Hunter	All specs
	Dash
Mage	All specs
	Healing Touch
Monk	Brewmaster	Windwalker	Mistwalker
	Survival Instincts	Bear Hug	Entangling Roots ?
Paladin	Holy	Retribution	Protection
	Rebirth	Wrath	Barkskin
Priest	Discipline & Holy		Shadow
	Cyclone ?		Tranquility
Rogue	All specs
	Growl
Shaman	Elemental & Enhancement		Restoration
	Solar Beam		Prowl
Warlock	All specs
	Rejuvenation
Warrior	Arms & Fury		Protection
	Stampeding Shout		Savage Defense ?

To understand the ability's full potential, watch the video below: