Stonesinger

Stonesinger is a Rift Guardian, a greatly empowered Sand Dweller. He can only be encountered as a random boss in a Nephalem Rift. As of patch 2.3, this Guardian was removed due to his ridiculously low difficulty, but after a revamp in 2.4, may spawn again in game.

In combat, he retains the Sand Dwellers' signature dust spellshield, gains increased damage of melee attacks (even more than other Rift Guardians, offset by his slow movement), and the following abilities:
 * Meteor Strike: summons a meteor to deal heavy Physical damage across the targeted area.
 * Turret: summons an immobile Fissure turret that fires Mortar projectiles until destroyed. These projectiles have a very small minimum range.
 * Charge: rushes to a random player outside melee range, dealing heavy Physical damage.
 * Knockback affix. A successful Knockback is often followed by an immediate Charge.

Development
The following ability was present on Stonesinger before 2.4:
 * Stone Unity: every 25% Life, Stonesinger split, forming +1 additional copy of himself (that is, one demon while above 75%, two until 50%, three until 25% and four while below 25%). Each additional Stonesinger dealt same damage and had same abilities. Cooldowns were not shared. They all had a single Life pool, however, effectively being bound by Health Link affix. Damaging one of the N monsters for X damage caused X/N damage to all of them. At 5% Life of lower, each demon stopped taking damage from others, but could share its own damage. Killing all of them would defeat the boss.

While the ability may sound dangerous, it actually made this boss one of the easiest possible Rift Guardians, effectively giving players with non-single-target skills the ability to damage all N copies at once, therefore multiplying all damage dealt by the player by N.

Interestingly, only one (original) Stonesinger would be displayed on minimap with a boss icon.