On the first tier of the Resto...yes, I said Resto...tree is a talent called Furor. With 5 points spent in this talent, you get a 100% chance of gaining 10 rage when shifting to Bear form and 40 energy when shifting to Cat form.
Powershifting is when a Druid takes advantage of the energy/rage gained by shifting out and back in to the same form.
First off, I know I mostly write about the tanking aspect of our Feral abilities, but powershifting is mainly used in our kitty form. However, if you're rage starved, powershifting works for Bear form as well, so we will discuss both.
Before we get into the dynamics of powershifting for Cat and Bear, lets first cover some tools to help you optimize your powershifting.
Since shifting forms requires mana, it is a must that you have some sort of add on that shows you how much mana you have. Let me tell you, it's quite embarrassing to be in the heat of battle, being awesome with your powershift skills, and then oops, you go to powershift and don't have enough mana to go back into form...then you have to stand there...in all our Cow-ish (or Elf-sih) glory, beating on the mob with your staff, and praying that Omen of Clarity procs before anyone sees you out of form. I can tell you with all certainty that when that happens...Omen of Clarity does not proc. Ever.
A few addons to help you keep an eye on your mana are Druid Bars, Simple Druid Bar, or Metahud, which is what I use (although I've noticed the mana bar is a bit buggy sometimes). I'm sure there are many other addons that show our mana bar while in form that you can look for so, experiment with several until you find one that you like.
Along with having a visual of your available mana pool, knowing when your next energy 'tick' is up is beneficial as well. We generate 20 energy every 2 seconds (if you search energy on WoWwiki, they say 30 energy every 2 seconds...I wish!!!). Since we want to optimize our energy gained and spend as little mana as possible, knowing if you're at the beginning or end of that 2 second tick in imperative. Some addons for keeping an eye on that 'tick' are Energy Watch v2, Energy Watch Countdown, or Energy Ticker. I haven't yet found my preferred mod for this as I'm still experimenting.
Shifting out and back into Cat form gives you 40 energy. This is not instant, though, as I've found there is a bit of delay, about 1 second, from when you powershift to when that precious 40 energy shows up on your bar. Since we normally gain 20 energy every 2 seconds; powershifting gives us twice as much energy in half the time. Basically, it's a 30 energy gain if you're at the beginning of your energy tick and a 20 energy gain if you're at the end.
This extra energy can boost your DPS. I'll quote from Elitist Jerks Feral Druid Mega Thread:
Over the course of two minutes or so, you should easily get around 125 energy (5 shifts worth, minus a few per shift for "imperfect" shifts) if you pay attention. 125/42 = ~3 extra shreds (126). 3 shreds at around 1500 damage each = 4500 extra damage without crits, or ~10000 damage with (40-80 DPS or so), plus 3-6 combo points (probably another 20-30 dps on it's own). Total DPS gain of around 70-80 or so, which is pretty nice.An increase of 70-80 damage per second over a 2 minute period is very nice! Granted, do to mana, you won't be able to powershift every time you're at zero energy on long boss fights, but you will still be able to boost your DPS output considerably.
For me, if I'm at the beginning of an energy tick, I don't mind powershifting if I have 10 or less energy. However, if I'm at the end of the tick, it doesn't seem worthwhile unless I'm at or dang close to zero.
The macro for powershifting in cat form is very simple:
/cast cat form
/y Powershift Cat!
The last line is optional and only adds a bit of silliness to, what I consider, a serious DPS increasing maneuver. It's fun to use in PvE, however I would advise against it while PvPing unless you just feel it necessary to taunt the enemy and see if they can 'catch' you in that split second of vulnerability.
You should rarely need to use powershifting in Bear form. The times that I have found it to be beneficial are when I'm rage starved, rooted, or needing a healing potion/healthstone.
When your in a situation where your not generating enough rage, powershifting can give that little boost to help keep aggro. This typically happens if you have over 30% dodge and you're running a non-heroic instance...heck, I've even had trouble generating rage in heroic instances. In these situations, powershifting can help get you a tiny bit of rage. It's not a cure all, but it sure helps when that third mob runs off to munch on your healer...powershift and charge it.
Yes, while tanking you are more vulnerable during a powershift than when you're shredding a mob from behind in cat form and there is more risk to doing this maneuver while tanking. However, if you're rage starved, it's because you're not getting hit enough and you're over geared for what you're doing. So, it's not going to hurt you much...if at all...to powershift.
There are also times when you get rooted and the mob runs off to either used ranged abilities on you or to munch on someone else. Powershifting is the fastest way to get out of your root and back onto the baddie.
Then, there are those times when you are challenged and you see your health getting lower and your healer is either dead, out of mana, or just unable to keep up. In these situations, powershifting with the addition of using a healing potion or health stone is called for. However, if you have a lot of rage, be sure to use Frenzied Regeneration before you powershift as you will lose that large pool of rage when shifting. Karthis over at Of Teeth and Claws wrote about using potions and stones in his Pots & Stones article. Please see his article for more information on using pots and stones as well as the macros for such. As for the basic powershifting macro...
/cast dire bear form
/y Powershift Bear!
Again, the last line is purely optional. ;)
A word of warning...do not powershift while in the midst of a global cooldown. If you do, you will come out of your current form and be left standing in either your Cow or Elf form. Not good and very frustrating when you're trying to optimize your play. Along with checking my mana, energy tick or rage status, I also glance down at my abilties to see where my GCD is before powershifting. Make this a habit!
If you're raiding and might be called upon to heal, Innervate, combat rez, etc. then be careful with how much you use your powershifting skills. Yes, it's fun to do...and I know sometimes it's easy to get caught up in damage meters and how you rate...but damage is not why Druids are brought to raids. If your raid leader wants pure melee DPS, they will bring a Rogue, not you. We are brought to raids because of our versatility. In one person, the raid gets a tank/off tank, an off healer, DPS, a combat rez, and an Innervate. If you spend all your mana powershifting so you can rank high on the damage meters, then you won't have the mana to combat rez the healer when you've got the boss down to 10%. So, use powershifting wisely.