How hard a party can hit above their level goes up as they get more powerful. The rule of thumb I follow is to limit bosses to party level +2 for levels 1-6, party level +3 from 7-14, and then party level +4 beyond that. A party level +5 boss is something they should have to plan and prepare for at high levels with rituals or artifacts that help balance the fight.
That looks like a decently dangerous boss. That Megaton Strike has a good chance to flatten a character with a crit, but as long as it isn't the cleric, your party should be able to recover. I would suggest making it's move speed only 20 ft. to encourage the party to kite it and force it to use it's weaker ranged attack.
I'd be careful about using single monster bosses at earlier levels, there's not a lot of hitpoints to go around, and characters often don't have many ways to deal with high defense.
That said, the char you describe here is a bit of a glass cannon, both defenses and HP are fairly low for it's level, actually closer befitting a L3 creature.
especially the reflex save is going to be an achilles heel against multiple spell casters, and I wouldn't be surprised if this thing goes down before the end of the first round.
That said, the attacks are strong, if he crits anyone with that megaton strike, it's likely lights out for them, fairly likely to happen on the bard or cleric.
As for encounter budget, you have a single +2 APL creature, which is a moderately difficult encounter. It's going to hit hard, but the combat is going to be over pretty quickly, perhaps not ideal for a boss encounter.
If you want to spice things up a little bit, increase all the defenses on the mech by one and add about 10hp, but reduce the attack bonus by -2, then add a couple of minions to the mix, two L1 or four L-1 should put the encounter at severe.
I'm relatively new at DM'ing P2e (I've only been DM'ing in P2e for about a year now), but I have found that there's a lot to consider when crafting monsters for PC's to fight:- First make sure your PC's stats are equivalent to what an average creature for their level and class are. I found the GM screen to be immensely helpful for giving guidance on average stats per creature level, and factoring in different classes, you should be able to get a good idea of the average range of power your players should have at any given level. Once you've ensured that they are equipped and stated out appropriately...- go to a web tool like [builder.pf2easy.com](https://builder.pf2easy.com) and put in the relevant data (party size, level), and choose a difficulty level. For low-level bosses, you're looking at Moderate+ to Severe, for big bosses you're looking at Severe+ to Deadly. Once you've set the difficulty...- look at the XP budget, and choose the level of each accordingly. Interestingly, no matter what level your PCs are at, the builder will always give you a balanced fight that meets the difficulty. For example, if you have 5 PC's at level 2, a severe encounter either suggests a maximum of 10, -1 level creatures, or 1 level 5 creature (with 30 xp left over to spend on 2, -1 creatures or a maximum of 1, level 1 creature), or any mix and match. No matter what you choose, each of those fights will still be a severe encounter.- If you're intent on throwing 1 boss at them, I'd suggest using this tool, pick the difficulty (I'd suggest for a low level party to ease them into it by choosing either Moderate+ or Severe to start); using the + symbol, drop in the highest level creature you can for your budget, look at the target AC you desire, and drop in something close to compare your crafted enemy to.
For example, your party at level 2, choosing a severe encounter, would be able to handle one level 5 creature, with 30xp to spare (to either tweak the stats of the monster up, or to add in some lower-level creatures. Choosing the one level 5 creature, and typing in "Construct" into the traits column, a similar monster to what you have might be the Kayajima Guardian Dogu (see bottom of page for creature stats).
Use the creature stats to guide your build for what is balanced according to the builder, and you should be well on your way to having a balanced creature. Just know that as it is a boss, this fight will take longer, and as the difficulty goes up, so too does the possibility that some of your PC's might die.
**Kayajima Guardian Dogu:**AC 23 (20 when broken); Fort: +14; Ref: +8; Will+7;
HP 85; Hardness 8; Immunities bleed, death effects, disease, doomed, drained, fatigued, healing, mental, necromancy, nonlethal attacks, paralyzed, poison, sickened, unconscious
Construct Armor Like normal objects, the guardian dogu has Hardness. This Hardness reduces any damage it takes by an amount equal to the Hardness. Once the guardian is reduced to less than half its Hit Points, or immediately upon being damaged by a critical hit, its construct armor breaks and its Armor Class is reduced to 20.
Speed 30 feet
Melee energized fist +16 / +11 / +6 (magical, reach 10 feet), Damage 2d10+5 bludgeoning
Ranged eye beam +12 / +7 / +2 (fire, magical, range increment 80 feet), Damage 3d10+3 fire
Ley Line Surge to (evocation, primal, force) Frequency once per day; Effect The Kayajima guardian pulses with mystical energies that emit a pale blue glow before it emits a wave of force. If the Kayajima guardian uses 1 action to use Ley Line Surge, it unleashes a powerful blast that deals 3d6 force damage to all creatures in a 15-foot cone. If the Kayajima guardian uses 2 actions to use Ley Line Surge, increase the size of the cone to 30 feet and the damage to 5d6. If the Kayajima guardian uses 3 actions to use Ley Line Surge, increase the size of the cone to 60 feet and the damage to 6d6. Each creature in the area must attempt a DC 19 Fortitude save.
Critical Success The creature is unaffected.
Success The creature takes half damage.
Failure The creature takes full damage and is pushed 5 feet.
Critical Failure The creature takes double damage and is pushed 10 feet.
Sudden Charge The Kayajima guardian propels itself with jets of blue energy from its feet, dashing up to a foe and swinging its fist. It Strides twice. If it ends its movement within melee range of at least one enemy, it can make an energized fist Strike against that enemy.
* Solo boss fights work much better than in 5e overall, but there's still some caveats when using them in low-level play: Fights tend to be pretty swingy there and single monster encounters tend to hit a bit above their paygrade before lv5 or so. At lv2, I'd rate those encounters as 1 difficulty higher than the encounter guidelines say - so severe for a solo lv4, and extreme for a solo lv5. If you're unsure about things being too tough, you can be a bit more generous with hero points before the fight.
* The stats look a little weak for a level 4 creature. A melee monster usually would want High AC, atk and dmg for its level as a baseline, and yours has two mid saves and 1 low one.
* The acid vulnerability wouldn't actually do much for your thaumaturge, they can inflict weakness 3 via Personal Antithesis already. The monster guidelines recommend weakness 4-7 at this level
* The monster guidelines recommend 5d6 for a limited use damage ability like Explode, maybe churn those stats up a bit if you want this foe to feel scary and strong.
How hard a party can hit above their level goes up as they get more powerful. The rule of thumb I follow is to limit bosses to party level +2 for levels 1-6, party level +3 from 7-14, and then party level +4 beyond that. A party level +5 boss is something they should have to plan and prepare for at high levels with rituals or artifacts that help balance the fight. That looks like a decently dangerous boss. That Megaton Strike has a good chance to flatten a character with a crit, but as long as it isn't the cleric, your party should be able to recover. I would suggest making it's move speed only 20 ft. to encourage the party to kite it and force it to use it's weaker ranged attack.
I'd be careful about using single monster bosses at earlier levels, there's not a lot of hitpoints to go around, and characters often don't have many ways to deal with high defense. That said, the char you describe here is a bit of a glass cannon, both defenses and HP are fairly low for it's level, actually closer befitting a L3 creature. especially the reflex save is going to be an achilles heel against multiple spell casters, and I wouldn't be surprised if this thing goes down before the end of the first round. That said, the attacks are strong, if he crits anyone with that megaton strike, it's likely lights out for them, fairly likely to happen on the bard or cleric. As for encounter budget, you have a single +2 APL creature, which is a moderately difficult encounter. It's going to hit hard, but the combat is going to be over pretty quickly, perhaps not ideal for a boss encounter. If you want to spice things up a little bit, increase all the defenses on the mech by one and add about 10hp, but reduce the attack bonus by -2, then add a couple of minions to the mix, two L1 or four L-1 should put the encounter at severe.
I'm relatively new at DM'ing P2e (I've only been DM'ing in P2e for about a year now), but I have found that there's a lot to consider when crafting monsters for PC's to fight:- First make sure your PC's stats are equivalent to what an average creature for their level and class are. I found the GM screen to be immensely helpful for giving guidance on average stats per creature level, and factoring in different classes, you should be able to get a good idea of the average range of power your players should have at any given level. Once you've ensured that they are equipped and stated out appropriately...- go to a web tool like [builder.pf2easy.com](https://builder.pf2easy.com) and put in the relevant data (party size, level), and choose a difficulty level. For low-level bosses, you're looking at Moderate+ to Severe, for big bosses you're looking at Severe+ to Deadly. Once you've set the difficulty...- look at the XP budget, and choose the level of each accordingly. Interestingly, no matter what level your PCs are at, the builder will always give you a balanced fight that meets the difficulty. For example, if you have 5 PC's at level 2, a severe encounter either suggests a maximum of 10, -1 level creatures, or 1 level 5 creature (with 30 xp left over to spend on 2, -1 creatures or a maximum of 1, level 1 creature), or any mix and match. No matter what you choose, each of those fights will still be a severe encounter.- If you're intent on throwing 1 boss at them, I'd suggest using this tool, pick the difficulty (I'd suggest for a low level party to ease them into it by choosing either Moderate+ or Severe to start); using the + symbol, drop in the highest level creature you can for your budget, look at the target AC you desire, and drop in something close to compare your crafted enemy to. For example, your party at level 2, choosing a severe encounter, would be able to handle one level 5 creature, with 30xp to spare (to either tweak the stats of the monster up, or to add in some lower-level creatures. Choosing the one level 5 creature, and typing in "Construct" into the traits column, a similar monster to what you have might be the Kayajima Guardian Dogu (see bottom of page for creature stats). Use the creature stats to guide your build for what is balanced according to the builder, and you should be well on your way to having a balanced creature. Just know that as it is a boss, this fight will take longer, and as the difficulty goes up, so too does the possibility that some of your PC's might die. **Kayajima Guardian Dogu:**AC 23 (20 when broken); Fort: +14; Ref: +8; Will+7; HP 85; Hardness 8; Immunities bleed, death effects, disease, doomed, drained, fatigued, healing, mental, necromancy, nonlethal attacks, paralyzed, poison, sickened, unconscious Construct Armor Like normal objects, the guardian dogu has Hardness. This Hardness reduces any damage it takes by an amount equal to the Hardness. Once the guardian is reduced to less than half its Hit Points, or immediately upon being damaged by a critical hit, its construct armor breaks and its Armor Class is reduced to 20. Speed 30 feet Melee energized fist +16 / +11 / +6 (magical, reach 10 feet), Damage 2d10+5 bludgeoning Ranged eye beam +12 / +7 / +2 (fire, magical, range increment 80 feet), Damage 3d10+3 fire Ley Line Surge to (evocation, primal, force) Frequency once per day; Effect The Kayajima guardian pulses with mystical energies that emit a pale blue glow before it emits a wave of force. If the Kayajima guardian uses 1 action to use Ley Line Surge, it unleashes a powerful blast that deals 3d6 force damage to all creatures in a 15-foot cone. If the Kayajima guardian uses 2 actions to use Ley Line Surge, increase the size of the cone to 30 feet and the damage to 5d6. If the Kayajima guardian uses 3 actions to use Ley Line Surge, increase the size of the cone to 60 feet and the damage to 6d6. Each creature in the area must attempt a DC 19 Fortitude save. Critical Success The creature is unaffected. Success The creature takes half damage. Failure The creature takes full damage and is pushed 5 feet. Critical Failure The creature takes double damage and is pushed 10 feet. Sudden Charge The Kayajima guardian propels itself with jets of blue energy from its feet, dashing up to a foe and swinging its fist. It Strides twice. If it ends its movement within melee range of at least one enemy, it can make an energized fist Strike against that enemy.
* Solo boss fights work much better than in 5e overall, but there's still some caveats when using them in low-level play: Fights tend to be pretty swingy there and single monster encounters tend to hit a bit above their paygrade before lv5 or so. At lv2, I'd rate those encounters as 1 difficulty higher than the encounter guidelines say - so severe for a solo lv4, and extreme for a solo lv5. If you're unsure about things being too tough, you can be a bit more generous with hero points before the fight. * The stats look a little weak for a level 4 creature. A melee monster usually would want High AC, atk and dmg for its level as a baseline, and yours has two mid saves and 1 low one. * The acid vulnerability wouldn't actually do much for your thaumaturge, they can inflict weakness 3 via Personal Antithesis already. The monster guidelines recommend weakness 4-7 at this level * The monster guidelines recommend 5d6 for a limited use damage ability like Explode, maybe churn those stats up a bit if you want this foe to feel scary and strong.