Achievement for killing all 4 slime tunnel bosses

game/modules/tome/data/achievements/kills.lua

@@ -243,3 +243,15 @@ newAchievement{
 	desc = [[Killed Linaniil, the Supreme Archmage of Angolwen.]],
 	mode = "player",
 }
+
+newAchievement{
+	name = "Fear of Fours", id = "SLIME_TUNNEL_BOSSES",
+	show = "full", huge=true,
+	desc = [[Killed all four bosses of the Slime Tunnels.]],
+	mode = "player",
+	can_gain = function(self, who, target)
+		self.nb = (self.nb or 0) + 1
+		if self.nb >= 4 then return true end
+	end,
+	track = function(self) return tstring{tostring(self.nb or 0)," / 4"} end,
+}

game/modules/tome/data/zones/slime-tunnels/grids.lua

@@ -42,6 +42,7 @@ local orb_summon = function(self, who)
 	local npc = game.zone:makeEntity(game.level, "actor", filter, nil, true)
 	local nx, ny = util.findFreeGrid(who.x, who.y, 10, true, {[engine.Map.ACTOR]=true})
 	if npc and nx then
+		npc.on_die = function(self) world:gainAchievement("SLIME_TUNNEL_BOSSES", game.player) end
 		game.zone:addEntity(game.level, npc, "actor", nx, ny)
 	end
 end