The Haken Büchse appears in the field in groups of two or three and sometimes alongside Fire Antiques. In the darkness, it morphs into the Coelacanth. One of these is found guarding the "X" that must be examined in order to engage in the second battle with Dolce, Guitar and Bass.
The normal attack is either an arm attack or a whacking tail attack. Its most powerful Special Attack is Crust Cracker, which is four hits of damage on all characters at melee range, including those standing behind him or to the side. Furnace Pellet is a piercing distance attack. Fiery Tail is a wide-range tail attack on all characters standing around him, while Sore Tail is a similar attack that it might use when its HP is low.
The Haken Büchse has rather high HP and some extremely powerful attacks. The fact that it can appear in groups of three means that the party could find itself in a dangerous situation if all three cluster together against the party. On the other hand, this can also be turned to the player's advantage by attacking more than one at the same time to quickly build Echoes. It may be worth considering trying to lure them into the darkness in order to morph it into the Coelacanth, which is rather less challenging, but also grants less EXP. Additionally, if any character is in Darkness Body status, they will morph the Haken Büchse into the Coelacanth if they attack at close range. One option is to begin the battle in darkness and have Salsa use a Shadow Silhouette on a Coelacanth when the other characters are close by, then build up Echoes and unleash a powerful Special Attack on the Haken Büchse. Alternatively, try to position her in the Haken Büchse's large shadow. Frederic can do a lot of damage with a well-powered Coup de Grace and also have a chance of causing knockback. Beat can also build up a lot of Echoes at a distance, while remaining away from the main fray of the battle.
In Encore Mode, these monsters can be extremely dangerous if their attacks are not Guarded against. Use the same basic tactics, but don't hesitate to have either Polka or Frederic heal if HP gets low. Build up Echoes and then unleash a powerful Harmony Chain to try to finish off these opponents.
- In the PlayStation 3 version of Eternal Sonata, the EXP gained for defeating a Haken Büchse was increased by 10 points, but its HP was greatly increased.