Once you hit level 60, two more optional polymorph spells open up to mages. Though no different from Polymorph: Sheep in the practical sense, the novelty and aesthetic of Polymorph: Pig and Polymorph: Turtle make these highly desirable mage spells.
Available through a simple level 60 quest chain.
Head to Archmage Xylem in Azshara (29, 40).
Accept the quest "Warlord Krellian." Kill the warlord. (41, 52)
Return and get the next quest, "Fragmented Magic." Sheep a bunch of Spitelash naga, they'll split into clones which will try to run quickly away. I found that you can polymorph and start AOE immediately to get the clones when they come up. (~32, 54)
Turn in. Get Polymorph: Pig.
Available through a Zul'Gurub boss drop. Zul'Gurub is an old 20-man level 60 raid.
Gahz'ranka is an optional boss of Zul'Gurub. He is level ??, which means that he is 3 levels higher than your highest team member only in the hit and resist percentage. So you might miss him some and he might resist some of your stuff, but otherwise he has the same health and attack power that he always had, and he'll die quickly under the guns of level 70s.
- Go into Zul'Gurub (a single well-geared person can do this part alone), head to Battered Tackle Box (left, through the water, up the hill left of the crocs, down into the water on the right, swim to Nat's camp) and have your 365+ skilled fisherman pick up the item inside (doesn't have to be a fisherman, but why waste it on a non-fisher?). Starts Nat's Measuring Tape, where you take the item to Nat Pagle (59, 60) in Dustwallow Marsh.
- The person who finished the quest can now buy Mudskunk Lures from Nat. Give them to your fisherman, if the buyer isn't your fisherman.
- Fish with the lures at any of the 5 spots of Muddy Churning Waters inside Zul'Gurub until your fisherman has 5 Zulian Mudskunks.
- People recommend clearing the deep pool south of Nat Pagle's Landing in Zul'Gurub and using a warlock's underwater breathing spell for your fight.
- Use the 5 Zulian Mudskunks to call forth Gahz'ranka. I've heard of people killing him with only 2-3 party members. So a decently geared level 70 party should have no problem at all.
- He knocks you up in the air and back, but otherwise I've read the fight is ridiculously easy.
- He has a 14% chance to drop Tome of Polymorph: Turtle, which is NOT bind-on-pickup. So you CAN sell it, trade it, or give it to someone else.
I really, really, really want to be able to use a macro to cast a random polymorph every time I have to polymorph something:
/castrandom [harm] Polymorph (Rank 4), Polymorph: Pig, Polymorph: Turtle
/emote randomly polymorphs %t.