The x2 button lets you toggle battle speed acceleration. It has three modes:

➡️ Battle speed x1 — characters fight at normal speed.

➡️ Battle speed x2 — characters fight twice as fast.

➡️ Battle speed x3 — characters fight three times as fast.

Battle speeds unlock progressively:

×1 — available from the start;

×2 — unlocked after completing The Dwarf Fort expedition;

×3 — becomes available after starting the Mungard expedition.