Use the item the nearby shop supplies
Buy a Bomb before starting the fight, then select it from Items. Its defense-piercing damage solves the low-HP, high-DEF enemy without relying on a basic weapon that Flying or Spiky can restrict. This is the base encounter; Hard Mode changes the enemy’s HP and incoming damage.
Mechanics references: Bomb · Spiky Killbot · Hard Mode
Do not plan around a later unlock
Dynamite is found farther into the mines, after this story encounter. It is not the first-visit solution. Annihilator stops selling Bombs after the Killbot is defeated, so that shop is an encounter-specific source rather than a permanent restock point.
Mechanics references: Snowy Thicket · Bomb
Stab and Rocket
Stab thrusts forward after a short preparation for 4 damage. Rocket deals 5 and can splash the party. Follow the projectile’s arrival; avoiding its direct hit also matters to your teammates.
Where it appears
The forced story encounter is in Snowy Thicket. A rematch appears on Pit Floor 18. Later weapon options can make that return easier, but those unlocks should not be assumed on the Chapter 1 visit.