Bone Prison

Creates a barrier of fossilized bone around your target.

Bone Prison is a level 24 Necromancer spell (Poison and Bone tree, requires Bone Wall and Bone Spear; it unlocks nothing). It summons a ring of bonewall segments around the targeted unit, trapping it and anything else inside the circle. The segments have no damage number: what levels buy is life, +25% a level past the first, so +475% at level 20, plus +8% per hard point in Bone Armor and Bone Wall. The ring stands 24 seconds at every level or until one segment breaks. The mana runs the other way from most skills: 27 at level 1, one less a level, 8 at level 20 and 1 from level 27 on.

The numbers

• Life is calc1, "HP % Modifier": Param1 25 ("HP % per level") times the level minus one, plus Param8 8 ("HP % synergy") times the hard points in Bone Armor and Bone Wall. 0% at level 1, +475% at level 20, +725% at level 30. The Basin's page writes the same rule as 25 × level − 25.
• Duration is Param2 600 frames at 25 a second: 24 seconds at every level, so it is left out of the table.
• Mana is 27 at level 1 and lvlmana −1 a level: 8 at level 20, 3 at level 25, and the tooltip's max(usmc, 1) holds it at 1 from level 27 on. The Basin's older page says a level 28 prison could be cast with no mana; the current table's floor (minmana 1) is 1.

The life bonus reads the full skill level (lvl), so +skills count; the synergy reads blvl, hard points only.

The base the percentage is applied to is the wall unit's own, which the Basin's page gives by difficulty: level 7 with 19 life and 35 defense in Normal, level 40 with 147 life and 174 defense in Nightmare, level 73 with 431 life and 334 defense in Hell. Its resistances there are 0 physical in Normal and Nightmare and 50 in Hell, 70, 90 and 90 cold, 70, 200 and 200 poison, with 0% drain and chill effectiveness, and a damage regeneration of 2.

How it works

Bone Prison is a cast construct: no attack roll, no damage, no state on the target. It is cast around the selected target rather than at a point. The Basin's rules for it:

• If there are obstacles or other units in the way when it is cast, there may be gaps in the ring through which the target can escape.
• It collapses when any single segment is destroyed or when the 24 seconds expire.
• Summon Resist does not apply to it, and friendly auras and buffs do not either; hostile auras do.
• It cannot be cursed, although Battle Cry and Cloak of Shadows still apply.
• It is summoned but it is not a pet: monsters that deal extra damage to pets deal their normal 100% to it.
• No experience is gained from monsters that die to Iron Maiden's returned damage while beating on the prison.
• It is not usable in town.

The cage is only as strong as its weakest segment. A monster that breaks one piece frees the whole pack, and in Hell the base life is 431 before the percentage, so the level and the two synergies are what hold the ring together.

Synergies and +skills

Two skills feed Bone Prison, each at +8% life per hard point (Param8 8), printed as two tooltip lines:

• Bone Armor: +8% Life per Level
• Bone Wall: +8% Life per Level

Both read blvl. In return Bone Prison is one of the tree's main synergy givers: each hard point in it feeds Teeth, Bone Spear and Bone Spirit's magic damage, Bone Armor's damage absorbed and Bone Wall's life, at the rates their pages show. A hard point here is worth +25% prison life and its share of those five lines; a +1 from items is worth the same +25% on the prison and nothing to the skills it feeds.

Against players

A prison deals no damage and casts no state on a player; it holds them inside the ring until a segment is broken or the 24 seconds expire, with the gap rule above. See Player versus Player.

Build notes

• At level 20 each segment has +475% life for 24 seconds at 8 mana; the duration does not grow, so points past the first are life and cheaper casts only.
• The twenty hard points a bone caster puts here feed Teeth, Bone Spear and Bone Spirit; they also make the prison a level 20 prison, with its own life rising further from hard points in Bone Wall and Bone Armor.
• The mana falls one a level, so at level 27 and past it the prison costs 1 mana: a utility cast with no mana budget at all.