There are lots of optional bosses dotted around in Mandragora: Whispers of the Witch Tree, none more annoying than the Chthonic Stalkers. There are three boss fights with them in the game, and if you find and defeat them all, then you’ll unlock the Tremors achievement.
Note: you’re going to need all the story-based upgrades to find and beat them.
Drakkeden Citadel
The first Chthonic Stalker fight is found in Drakkeden Citadel. You’ll need the Grappling Hook to reach it, but you won’t be able to access this area in the game without it, so you should be fine.

Starting from the Lower Citadel Witch Stone, you’ll want to head left towards the purple area of the map. Continue all the way left until you reach this grapple point.

Straight over the top and you’ll find yourself in the Chthonic Stalker room. It always starts with a floor slam that will send out a shockwave, so get ready to jump (and don’t get too close, because its head has a hitbox).

Forgotten Catacombs
To reach the Chthonic Stalker in the Forgotten Catacombs, you’ll need access to the Double Jump, which you receive after beating the main boss in Drakkeden Citadel.
Starting from the Forgotten Catacombs Witch Stone, head right and up until you reach here on the map.

You’ll need the double jump here to clear the gap and reach the far right part of the path.

At the bottom of this path, there’s a trap right before the boss room, and a portal. As you have the double jump, you can enter the portal and it’ll take you to another Witch Stone (Catacomb Depths), which is very handy for respawning if you’re struggling with Chthonic Stalker number 2!



If you rest at the Catacomb Depths, you can just double jump back up through the portal, and you’ll be right back at the boss fight. Only one fight left to unlock the Tremors achievement!
Braer Castle
Fittingly for the hardest Chthonic Stalker encounter, you’ll need the final upgrade in the game to find the fight – the glide ability. You get this after defeating the Sleepwalker, so you’ll hopefully be kitted up enough for the very tough optional boss encounter here.

Starting from the Braer Castle Left Wing Witch Stone, head left and go through the door just past the two ruined sets of armour.
Head all the way down to the basement – watch out for the slimes and bloodfiends dropping from the ceiling! – until you reach a large gap filled with green slime.

You’ll need to double jump and glide to cross this, and the boss is very close to the other side. Healing is highly recommended before jumping over (using some food or bandages, keep your flasks for the fight).

This boss fight contains two Chthonic Stalkers at once – try and get them both on the same side of the arena and keep them together so you don’t get caught in a charge loop from both sides. When they burrow underground, you can avoid all damage by jumping and gliding over the attack – don’t try and dodge through it. You will be stunned.

Once you’ve taken all 3 of the Stalkers down, you’ll unlock the Tremors Achievement! Congratulations!
If you’re looking for more optional bosses and achievements in Mandragora, we also have one for the Queen of Smiles here!