Headhunter I.D. Challenge Feasibility adjustments:

Spawns demoted to random_elites (with 2 classes, drop 2 rares).
Killing a target spawn causes all other NPC's to pause and untarget the player.
Npcs lower than elite rank, or summons from a target spawn, may be killed without failing the quest.
Spawns may be killed by party members or summons of party members, otherwise the quest will fail immediately if a spawn is killed by something else, or if the player exits the level.

Fixed a bug in Mirror-Match boss placement.

game/modules/tome/class/GameState.lua

@@ -2675,7 +2675,7 @@ function _M:infiniteDungeonChallengeFinish(zone, level)
 		end
 	elseif id_challenge == "mirror-match" then
 		local x, y = self:findEventGrid(level, function(self, level, x, y)
-				if x > 10 and x < level.map.w-10 and y > 10 and y < level.map.h and self:canEventGrid(level, x, y)then return x, y end
+				if x > 10 and x < level.map.w-10 and y > 10 and y < level.map.h-10 and self:canEventGrid(level, x, y)then return x, y end
 			end
 			)
 		if x and y then
@@ -2791,24 +2791,23 @@ function _M:infiniteDungeonChallengeFinish(zone, level)
 			end)
 		end end, "Refuse", "Accept", true)
 	elseif id_challenge == "headhunter" then
-		local mlist = {}
+		local mlist = {} -- add random elite "spawns of Urh'Rok"
 		for i = 1, rng.range(2, 4) do
-			local m = zone:makeEntity(level, "actor", {type="demon", random_boss={
+			local m = zone:makeEntity(level, "actor", {type="demon", random_elite={
+				ai = "tactical",
+				life_rating=function(v) return v * 1.3 + 3 end,
 				nb_classes = 2,
-				rank=3.5, ai = "tactical",
-				life_rating=function(v) return v * 1.5 + 5 end,
-				loot_quantity = 2,
-				no_loot_randart = true,
+				loot_quantity=2,
+				nb_rares=2, -- make this difficult challenge (usually) worth trying and failing
+				no_loot_randart=true,
 				name_scheme = "#rng# the Spawn of Urh'Rok",
 			}}, nil, true)
 			if m then
-				local x, y = rng.range(1, level.map.w - 2), rng.range(1, level.map.h - 2)
-				local tries = 0
-				while not m:canMove(x, y) and tries < 100 and not level.map.attrs(x, y, "no_teleport") do
-					x, y = rng.range(1, level.map.w - 2), rng.range(1, level.map.h - 2)
-					tries = tries + 1
+				local x, y = self:findEventGrid(level, function(self, level, x, y)
+					if x > 0 and x < level.map.w - 2 and y > 0 and y < level.map.h - 2 and m:canMove(x, y) and self:canEventGrid(level, x, y) then return x, y end
 				end
-				if tries < 100 then
+				)
+				if x and y then
 					m.is_headhunter_npc = true
 					zone:addEntity(level, m, "actor", x, y)
 					mlist[#mlist+1] = m
@@ -2816,26 +2815,52 @@ function _M:infiniteDungeonChallengeFinish(zone, level)
 			end
 		end
 		if #mlist > 0 then
-			Dialog:yesnoPopup("Challenge: #PURPLE#Headhunter", "Kill all "..#mlist.." spawns of Urh'Rok on the level and no other creatures, for a reward.", function(r)
+			Dialog:yesnoPopup("Challenge: #PURPLE#Headhunter", "Kill "..#mlist.." spawns of Urh'Rok on the level before killing any other elite (or higher rank) creatures, for an uncommon reward.", function(r)
 				if not r then
-					local q = self:makeChallengeQuest(level, "Headhunter", "Kill all "..#mlist.." spawns of Urh'Rok on the level and no other creatures.", {
+					local quest = self:makeChallengeQuest(level, "Headhunter", "Kill "..#mlist.." spawns of Urh'Rok on the level before killing any elite creatures.", {
 						dynamic_desc = function(self, desc)
-							desc[#desc+1] = ("%d / %d spawns killed."):format(self.nb_killed, self.to_kill)
+							desc[#desc+1] = ("%d / %d demon spawn killed."):format(self.nb_killed, self.to_kill)
 						end,
-						nb_killed = 0, to_kill = #mlist,
+						nb_killed = 0, to_kill = #mlist, mlist = mlist,
 						on_kill_foe = function(self, who, target)
 							if self:isEnded() then return end
-							if target.is_headhunter_npc then
+							if target.is_headhunter_npc then -- killed target spawn
 								self.nb_killed = self.nb_killed + 1
+								game.bignews:say(60, "#ORCHID#You claim the head of "..target.name..", giving pause to all foes on the level.")
 								if self.nb_killed >= self.to_kill then
 									who:setQuestStatus(self.id, self.COMPLETED)
 								end
-							else
+								for uid, e in pairs(game.level.entities) do -- other enemies pause, untarget player
+									if e ~= who and table.get(e, "ai_target", "actor") == who then
+									e:setTarget()
+									e.energy.value = -game.energy_per_tick
+									end
+								end
+							elseif target.rank >= 3 and (not target.summoner or not target.summoner.is_headhunter_npc) then -- killed forbidden target
 								who:setQuestStatus(self.id, self.FAILED)
 							end
 						end,
+						on_exit_check = function(self, who)
+							if who.dead and not self:isEnded() then who:setQuestStatus(self.id, self.FAILED); return end
+						end,
 						forbid_rewards = {"randart", "stat_pts", "generic_pt"},
 					})
+					for _, m in ipairs(mlist) do
+						m.id_challenge_quest = quest.id
+						m.on_die = function(self, src)
+							local p = game:getPlayer(true)
+							local q = p:hasQuest(self.id_challenge_quest)
+							if src ~= p and q then
+								src = src and src.summoner or src
+								if game.party:hasMember(src) then -- killed by player, party member or related summon
+									q:on_kill_foe(src, self)
+									return
+								end
+								-- killed by something else, quest fail
+								p:setQuestStatus(q.id, q.FAILED)
+							end
+						end
+					end
 				else
 					for _, m in ipairs(mlist) do m:disappear() m:removed() end
 				end