Keeping with the Rogue Trader RPG/Warhammer 40k theme of my particular Iron Gods campaign the Robot Warden is replaced with a Castellax Battle Automata. My players faced off against this guy yesterday. The fact he started 240 feet away (which was its kill zone) caused lots of problems for the melee centric party. Though he didn’t last long when they finally got into melee range he was around a lot longer than other creatures of the same challenge like the Mutant Manticore. The battle last seven rounds which is about double average for a D&D 5e battle. My players also tried to trick/convince it to override its programming so every time they succeed at an opposed Charisma check I had it lose one of its attacks. Spur of the moment thing.
CASTELLAX-CLASS BATTLE AUTOMATA
Large construct (robot), unaligned
Str 29 (+9) Dex 14 (+2) Con 20 (+5)
Int 10 (+0) Wis 18 (+4) Cha 10 (+0)
Saving Throws Str +14, Con +10, Wis +9, Cha +8
Skills Cybertheurgy +8, Athletics+ 14, History +8, Perception +9
Damage Resistances bludgeoning, piercing, and slashing from nonmagical weapons that aren’t adamantine.
Damage Immunities force, necrotic, poison, psychic
Condition Immunities charmed, frightened, paralyzed, petrified, poisoned, stunned
Senses Darkvision 60 ft., passive Perception 19
Challenge 13 (10,000 XP)
Gift of the Machine God. As a creature of technology a deformed android gains many damage and condition residences and immunities but they are also susceptible to electrical attacks.
Spotlight. As a bonus action, a Castellax automata can target a single creature with a beam of strobing light that functions as a gaze attack with a range of 60 feet. A creature subject to this attack must succeed at a DC 17 Constitution save or become blinded. Creatures with light blindness or light sensitivity take disadvantage on the saving throw.
Infrasonic Field. Castellax automata constantly emit powerful sound waves at a frequency below normal hearing. These vibrations can debilitate living beings within melee range. Such creatures must succeed at DC 17 Constitution save or fall prone and be nauseated until a save cancels. A warden robot can suppress or resume this ability as a free action.
Reactive Armor. A Castellax automata is covered in a special shell that reacts explosively to powerful strikes. Due to this covering, a warden robot gains light fortification (25% chance to negate critical hits and sneak attacks). When the armor negates a critical hit from a melee weapon, the attacker takes an amount of fire damage equal to half of the damage dealt to the robot. Attackers using reach or ranged weapons avoid this damage.
Resilient. Castellax automata receive a +3 racial bonus on all saving throws. They also hardened to resist lightning attacks eliminating the robots weakness to lightning.
Multiattack. Castellax automata makes two attacks of its choice from boltor and shock charger fists.
Shock charger fist. Melee Weapon Attack: +14 to hit, reach 10ft., one target.
Hit: 30 (6d6 + 9) lightning damage.
Boltor. Ranged Weapon Attack: +14 to hit, range 60/240 ft., one target.
Hit: 35 (4d12 + 9) explosive damage.
Mauler Pattern Bolt Cannon (Recharge 5-6). The Castellax can fire a barrage of boltor fire at a specific point it can see within 500 feet of it. Each creature within 10 (2 creatures) feet of that point must make a DC 17 Dexterity saving throw, taking 54 (12d8) explosive (fire and force) damage on a failed save, or half as much damage on a successful one.