Metin stones are the reason the game is called Metin2. They fall from the sky, sit exactly where they land, and cannot chase you or hit you back. What they can do is spawn wave after wave of monsters on whoever is attacking them, which is why a metin fight is usually a fight against everything standing around it. They are also the main source of skill books, spirit stones, and soul stones in the game, so nearly every progression path runs through them.
How a metin fight works
Metins are class 5 opponents, which makes them considerably harder than a normal monster of the same level. They do not move and do not attack directly. Instead, depending on the metin and how much HP it has left, a metin spawns around ten groups of monsters that attack whoever hit the stone. The pattern is regular: the first two spawns are one group each, the next four are two groups, and the last four can be up to three groups. The fight gets harder the closer the stone is to breaking.
The rule of thumb for drops is to break metins no more than nine levels above your own. Farming a stone far above your level is slow, dangerous, and does not pay better.
If you have one, a Metin Stone Spawner can summon a metin without waiting for a respawn.
What they drop
Almost every metin in the game can drop a Skill Book, with three exceptions: Metin Pung-Ma at level 75, Metin Ma-An at level 80, and Metin Tu-Young at level 85. Those three do not drop books at all.
Spirit Stones start dropping at Metin of Black, level 25, and from any metin above it. Metins inside dungeons are the exception.
Soul Stones need a metin above level 40. Metin of Soul is the first one that can drop them.
The bonus "Strength against Metin stones" applies to all of them, so if you are farming seriously that is the stat to look for on gear.
Where the main metins are
The early stones are packed into the three starting maps, so you never have far to walk.
- Metin of Sorrow (5), Metin of Combat (10), Metin of Battle (15), Metin of Greed (20): Joan, Pyungmoo, and Yongan.
- Metin of Black (25): adds Bakra, Bokjung, and Yayang.
- Metin of Darkness (30) and Metin of Jealousy (35): Bakra, Bokjung, Yayang.
- Metin of Soul (40): Yongbi Desert. First stone that can drop a soul stone.
- Metin of Shadow (45): Valley of Seungryong and Yongbi Desert.
- Metin of Toughness (50): Yongbi Desert, and also inside Demon Tower.
- Metin of Devil (55) and Metin of Death (65): Mount Sohan, plus Demon Tower.
- Metin of Murder (70): Doyyumhwan and Demon Tower.
- Metin Pung-Ma (75) and Metin Ma-An (80): Land of Giants and Lungsam.
- Metin Tu-Young (85) and Metin Jeon-Un (90): Red Forest.
Respawn and spawn counts
Spawn density varies by map. In the three starting maps, Metin of Battle allows up to six stones per map and channel, while Metin of Combat and Metin of Greed allow up to two. The wiki documents up to three Metin of Black stones per map and channel in Joan, Pyungmoo and Yongan with an average respawn of about 15 minutes, and lists separate spawn locations for Bokjung, Bakra and Yayang. Metin of Black can also be summoned from a Metin Stone (L).
Stone grades and socket slots
If you are farming stones to socket into gear, the metin's level changes the grade of the stone, not the chance of getting one. Third party data compiled from the base server files puts the drop chance around 60 percent across metins, with the grade distribution shifting upward as the metin gets stronger. Metin of Black averages about a +1.2 stone, Metin of Toughness about +1.6, and Metin of Murder about +2.1. A +4 stone almost never appears on a low level metin, so farming low stones hoping for a high grade is a waste of time.
Weapons and body armour take three stone slots each. Helmets and shields take one. Bracelets, boots, necklaces, and earrings have no stone slot at all, so those improve through bonuses and upgrading instead. Accessories run their own separate slot system with its own attach chances and durations.
Those numbers come from the base server files. Private servers set their own rates, so check your server before building a farming plan around them.
Sources
[1] Metin2 Wiki: Metin list, spawn areas and drop categories
[2] Metin2 Wiki: Metin of Black
[3] Metin2 Wiki: Metin of Combat
[4] Metin2 Wiki: Metin of Greed
[5] Metin2 Wiki: Metin of Battle
[6] Metin2 Atlas: Stone sockets and drop grades