Dragon

1000 Hit points
700 Experience points per kill

Knights: Only one knight should be present in a team hunt, as they, the blocker, must be able to move freely around the dragon and to maintain their diagonal position as the dragon takes a step (players sometimes call this "dancing with the dragon."). Also, it is wasteful to have two knights blocking, as they will both be damaged by the dragons' fireballs. It is quite easy for a Knight of level 40 or higher to block a dragon without using any Health Potions at all.
The knight's job in a team hunt is to prevent the dragon from attacking the shooters or retreating, when wounded, into any narrow spaces. To keep your consumption of healing supplies at a minimum, do not try to use two blockers, as stated above; the fireball attack will burn both of them.
Around level 40, a knight with good skills and, optionally, a Two-Handed weapon can solo a dragon (however, the knight should be prepared to use several potions). A shield is not critical as melee is generally the dragon's weakest attack, thought it should be considered that it is constant, happening every two seconds. Again, stand diagonal to it and always be prepared to use potions. If you have some spare mana you can use some exori hurs to speed up the kill. Knights with an attack skill of 80 and around 1000 hitpoints can easily kill a Dragon with a good Two-Handed Weapon (preferably a Giant Sword or, if you can get it, an Avenger).
Mages of level 28 or higher can kill dragons without help from other players. They can Summon two Demon Skeletons and drink a few extra mana potions afterward. They should try to keep enough mana to use exura gran or exura vita, if needed. They should enter, lure the dragon out, attack it with the demon skeletons, then move to a different floor so the dragon will target the demon skeletons. After waiting about 2 seconds, they should then come back and attack the dragon again, so that the demon skeletons will attack it and keep it from moving. It is advisable to move to a space about 3 squares diagonal and use a strike spell (exori frigo if possible) or icicle runes to kill the dragon faster. This is absolutely the cheapest way for a low-level mage to kill dragons; however, higher levels do not need demon skeletons' aid. If the dragon flees into a narrow tunnel, it is an option to cast mana shield, find the dragon, and use Sudden Death Runes on it before it heals itself and drains your mana with Fire Wave. A druid of level 33 or higher can solo a dragon in a similar way to a Knight, by using a Hailstorm Rod and exura gran and staying diagonal to the dragon.
A druid of level 36 (or higher) can use the Mass Healing spell, which allows druids to heal their summoned demon skeletons for 150 mana. Using dragon hams as a food source (supplemented by food brought by the player) and being skilled enough to avoid the dragons fire attacks, a druid of level 36 or more can hunt dragons for next to no cost easily.
Around level 50, mages can efficiently use exori frigo only to kill it. Heal when your hp drops under 280-300. You can take some icicles with you in case the dragon flees into some narrow cave.
(Note: Sorcerers CAN solo a SINGLE dragon spawn at level 19 with Wand of Decay, but it is a waste as it requires 6-10 mana potions for healing. Be sure to avoid the Fire Wave and try to keep health above 200.) Note: all mages should always keep full defense mode on, since dragons' melee is very strong