These achievements cannot be missed, as they are required to progress the game.
Soulreaper
Fight Soulreaper
The very first boss “fight” in the game, and the only one you’re expected to lose.
Esgonian general
Defeat Esgonian general
The main boss of Brocleyshire.
HMWV
Defeat HMWV
The “mid-boss” of Mid Mythrilia. Not recognized as a boss on map.
Maximillian II
Defeat Maximillian II
The first boss of Mid Mythrilia.
Kumasith
Defeat Kumasith
The second boss of Mid Mythrilia.
Headless horseman
Defeat Headless horseman
The first boss of the Wesandyth Kingdom.
Santiago
Defeat Santiago
The second boss of the Wesandyth Kingdom.
Duel
Stop Soulreaper
The second boss of the Northern Border. The second fight with the Soulreaper.
Ground shaker
Defeat Ground shaker
The first boss of the Glizzian Area.
Shroom prime
Defeat Shroom prime
The second boss of the Glizzian Area.
Valerie
Defeat Valerie
AKA Dragon Bones. The second of The Void’s three final bosses, after the Soulreaper’s third fight.
In addition to the game’s proper normal and true endings, there are also five bad endings corresponding to specific bosses listed above.
If you already defeated any of the bosses without reaching their respective bad ending (assuming you saved past their fight), you won’t be given another chance to get their bad ending until New Game+.
The count of piety
Failed to defeat Santiago
Dying to either form of Santiago will give this bad ending. Although Santiago’s attacks are generally easy to read and dodge, the Count of Piety’s homing lightning pillars, giant electric spheres, and The Devourer’s electricity beam can easily kill you and net this achievement.
Kumasith rampage
Failed to defeat Kumasith
The bear doesn’t have an attack that hits nearly as hard as Maximillian II’s bone wave, so this bad ending is easy to miss.
Soulreaper reborn
Defeat Soulreaper
You will get this bad ending if you manage to defeat the Soulreaper on the very first fight against her. It’s possible, albeit potentially time-consuming to get this achievement without New Game+ due to her bulk and high damage this early in the game.
As for what happens next?
Dominator Holborn
Failed to stop Soulreaper
This bad ending is obtained by dying in the second fight against the Soulreaper. It’s very easy to achieve as the Soulreaper can potentially one-shot you with many of her attacks in her second phase, or even in the shockwave transitioning to it!
Evolving fungus
Failed to defeat Shroom prime
Shroom Prime is a relatively passive boss, and doesn’t hit particularly hard at this point of the game. Unless you stay inside the left mushroom’s poison clouds long enough, this bad ending is the easiest to miss.
Note that you must die in the plot-mandated fight versus Shroom Prime; you cannot use its Rift fight, as that will just give the normal game over.
Family reunion
Achieve normal ending
Defeat the final bosses without going through the required steps for the true ending. The normal ending is distinguished by the post credit scene where Vivian’s parents, Valerie, and Vivian disappear from the family dinner memory.
Seed of life
Achieve true ending
To summarize the process of obtaining the true ending:
The true ending is distinguished by the post credit scene where Vivian is brought back to life from The Void because of the Mother Bear-blessed seed’s sacrifice, which is then planted and grows into a sapling.
Fallen Kumasith
Defeat Fallen Kumasith
Aka Wraith of Kumasith. If you’re going for the true ending, you can’t miss this achievement.
Very hard mode
Clear the game in Very Hard difficulty
The game has four difficulties as of this writing: Normal, Hard, Very Hard, and Lunatic. These difficulties change how much damage enemies inflict, but otherwise don’t appear to do anything else. With some patience, it’s possible to finish a fresh game on Very Hard; another option is to change difficulties to Very Hard on New Game+, as the damage difference won’t be game-changing until The Void. I’m not sure if Lunatic saves can unlock this achievement; given the wording, it’s better to assume not.
Achievements related to filling out parts of the in-game Note section, or completing a collection.
Explorer
Activate all Stelas
The ‘Stelas’ are one type of the save points scattered through out the game. Once you interact with a Stela (exploring a room with a Stela is enough to count towards the achievement), you can warp back to that room from another Stela. The majority of the game’s Stelas can’t be missed as they’re positioned along the main story path, with the exception of the Dungeon of The Decayed and the Shadow Path. There are 18 Stelas found across the game’s 6 regions:
True runeswarden
Acquire all skills
With the exception of Impulse Blade and Dimensional Swords, all skills are learned by acquiring their corresponding Stone Plate. There are 10 skills in total:
Gourmet
Acquire all recipes
To unlock a recipe, you must purchase the food from a chef. There are 12 recipes distributed among the 6 regions’ chefs:
Slayer
Unlock all entries in Monsterpedia
There are 80 different monsters to kill in the game, including the 19 bosses, a few monsters that spawn exclusively from bosses, and the Hen. You can always go back to fight some of the bosses again through their Rift; this is particularly helpful with filling in the Groundshaker Grub’s entry, as it can glitch out and spawn in an ‘unkillable’ state in the normal Groundshaker fight, which never happens in Groundshaker’s Rift (mind the Rift grubs’ bulk).
Runecraft master
Unlock all abilities
This includes all of Runeswarden’s levels; without extensive mana farming (see Mana collector), you’ll likely have some locked Abilities when you reach the final bosses.
Noted
Unlock all entries in Note
Specifically, the Journal part of Note. You can’t miss this achievement as you finish the game with either ending.
Other collection-based achievements focused on obtaining specific items, gold, or mana.
Wealthy traveller
Collect 1000000 gold
Mana collector
Collect 1000000 mana
These two achievements can be done concurrently by grinding early game at the Throneroom, mid game in the Magnus Workshop Rift and Shroom Prime’s Rift, and late game at two specific rooms in The Void:
Enhanced
Acquire a max ranked weapon or armour
To clarify, this means any weapon or armor drop that’s already at the max 5 star rank. You’ll inevitably get this achievement as you play, whether from monster drops or opening chests. It doesn’t matter if there are runes inside the equipment or not, only the ‘natural’ drop rank matters.
The truth
Acquire Sword of verum
The Sword of Verum is the final reward of the Dungeon of the Decayed, after defeating Vivian’s Shadow. At max rank, it has 400 attack and the fastest attack speed of all weapons in the game.
Enhanced
Acquire a weapon or armour with 4 runestones
The older ‘brother’ of Enhanced. As with that achievement, you must find a weapon or armor drop that is already at max rank, but the equipment’s slots also have to contain 4 runestones in it already. If this sounds like an obnoxious RNG achievement, that’s because it is.
The rest of the achievements that don’t fit anywhere else.
Gone waste
Keep drinking potions
You know how there’s a potion ‘cooldown’ that severely reduces the effect of potions consumed in that timeframe? If you keep drinking potions in spite of the cooldown, you’ll unlock this achievement.
Potion fever
Consumed 100 potions in total
Self-explanatory.
Demon hunter
Slay 666 monsters
Also self-explantory. You could speed up this achievement’s progress early on with enough farming.
Mastery
Achieve 100 combos
Mastery
Achieve 500 combos
Chain burst
Achieve 999 combos
These three combo achievements can be slowly, but safely obtained by wailing on the infinite health training dummy in Bluereel Village. (Advanced) Mirage Storm helps a lot with the combos as it does a sizable number of multi-hits overtime, and has a lower rage cost than Tornado Slash.
I killed the chicken
Slay the chicken
Just kill one of the (abnormally bulky) Hens wandering Brocley village. They don’t fight back and only run off after being attacked once, and any attack will juggle them. If you’re trying to unlock Slayer, you can’t miss this achievement. No, nothing else happens after killing one of the Hens.
Onion!
Acquire an onion from the chef in Brocley village
At the very beginning of the game, keep talking to the man outside the door to Brocley village’s cafe, and he’ll give you a free onion and this achievement. You can only do this before the first fight against the Soulreaper!
The Vagrant
Unlock all achievements
Unlock every other achievement in the game. Good luck!