A quick beam of lunar light burns the enemy for (20% of Spell power) Arcane damage and then an additional (156.6% of Spell power) Arcane damage over 18 sec.
It was originally considered an excellent choice for pulling, regardless of the druid's specialization due to its instant cast and long lasting DoT.
However in Shadowlands retail edition, a more recent practice is to first pre-cast [Wrath] before casting this spell, as Wrath has a cast and travel time and so makes efficient use of time out of combat, whereas Moonfire would hit instantly and draw aggro.
[Sunfire] and Moonfire both apply most of their damage over time (known as a DoT effect). When targets would die quickly (eg, before the DoT runs its full duration) it may not be worth spending the GCD on this spell, as this gets little damage out of the DoT component and others spells may be more effective.
If an enemy is at low health you can finish them off by spamming several Moonfires or Sunfires in a row. This is low DPS, but as instant-cast spells this can be done on the move to a fleeing enemy or in PvP.
Trivia[]
Moonfire is a basic Druid spell in Hearthstone. The flavor text reads: ""Cast Moonfire, and never stop." - How to Be a Druid, Chapter 5, Section 3"
Now has a base duration of 20 seconds (up from 14 seconds), but is no longer extended by [Starfire] and [Starsurge] critical strikes. Upon reaching 100 Lunar Energy, the next Moonfire deals 100% additional initial damage.
Moonfire and Sunfire will now replace each other on the Action Bar when switching cycles on the Eclipse Bar.
Patch 5.0.4 (2012-08-28): No longer generates any Energy or changes into Sunfire while in Solar Eclipse. Duration increased from 12 to 14 sec. Now learned at level 3 (was 4).
Hotfix (2011-07-19):Moonfire will now generate Lunar Energy when crossing from Solar to Lunar on the Eclipse bar.
Patch 4.0.6 (2011-02-08): Now costs 9% of base mana, down from 18% of base mana.
Patch 4.0.1 (2010-10-12): Now lasts 12 seconds (was 9) and has a 40 yd range (was 30).
Patch 3.0.8 (2009-01-20): Moonfire has a new spell animation.
[Moonfire].
[Celestial Guardian], 
[Cosmic Rapidity], 
[Denizen of the Dream], 
[Dying Stars], 
[Galactic Guardian], 
[Gore], 
[Moonless Night], 
[Protector of the Pack], 
[Shooting Stars], 
[Wrath] before casting this spell, as Wrath has a cast and travel time and so makes efficient use of time out of combat, whereas Moonfire would hit instantly and draw aggro.
