As you all know, +100 hp to head is a very wanted "enchant" to get for your twink (You can also use it for your main, but it's a more coveted twinking item). However, many a time I see "omg where you get that +100 hp to head? Is that from an enchanter? Please tell me."
As a matter of fact, you need to do a quest for it. The quest is called "Libram of Constitution" and is located in Burning Steppes (Eastern Kingdoms).
For starters, you will need to have 30 gold. twocents
The next things you will need are as follows:
[Black Diamond] x1
[Lung Juice Cocktail] x1
[Libram of Constitution] x1
[Night Dragon's Breath] x4
How do you get these items you ask? Well here's a little guide to make this quest go by a bit faster for your convenience.
First, Night Dragon's Breath can be acquired in Felwood. Depending on whether you're Alliance or Horde, you'll have to talk to the appropriate NPC to begin the Cleansing of Felwood, which will involve you killing the Warpwood Shredders in the northern part of the zone to collect shards. The Horde NPC that begins this quest is right off the road, a little further north than the druid tents and to the left. Once you've completed this first stage, you'll be given a Cenarion Beacon (hang on to this, you'll need it to collect corrupted soul shards!).
Now you must collect six corrupted soul shards and in exchange, you'll receive two salves (And you need four to collect night dragon's breath). Corrupted soul shards have a chance to drop off any mob in the zone. Once you have four salves, you can cleanse the night dragon's breath plants. They are located at the following coordinates:
1st Location: 35,60
2nd Location: 50,30
3rd Location: 40,78
4th Location: 42,13
Once you've cleansed the plant, you can collect the dragon's breath (usually yields 4-5 per use). Once you've collected from a plant, it takes about a half an hour before you can collect again. The nice thing is, if you hang around and wait, you can just keep collecting, you don't need any more salve! So you can usually just hang around and keep collecting from the same plant.
The rest of the quest is easy. Hop on over to the Blasted Lands (Horde have a flight path to Stonard in Swamp of Sorrows, Alliance has Nethergard Keep right in the zone I believe). A Blood Elf in the ruins near the entrance gives the quest for the lung juice.
The scorpids are right near the entrance with the hyena's and vultures and the drop rate is fairly high. A little further south near Defiler's Rise you can find the basilisks, who also have a fairly high drop rate, along with hellboars, who's drop rates are quite a bit lower (This is what you'll be grinding on for the longest time). Remember when you're grinding, the hellboars, basilisks, and felhounds all share the same spawn point, so kill everything, it'll keep the hellboars respawning much quicker! There's also another variety of boar further east that will drop the blasted boar lungs as well. Once you've gathered everything, hope back over to Mathredis and you're done!
The Libram of Constitution can simply be found in the AH. It's dropped by many different mobs in many different locations so I couldn't really post a specific area to farm for it. Black Diamonds can also be purchased off the Auction House, or they can be dropped off mobs in BRD.
That's all there is to it. If you know of an alternative way, please feel free to post it. Enjoy