Abandoned Temple

In Abandoned Temple Area 1, defeat Garm enemies to progress Quest 73. This quest does not need to be submitted immediately.

Note that the western stairs in Area 1 are a dead end, even if accessed via a shortcut. Your objective is the eastern stairs to proceed.

In Abandoned Temple Area 2, the only path forward is via the westernmost stairs, which lead to a previously inaccessible area in Area 1.

The boss fight is located directly north of the entrance at approximately X:12 Y:3. You could not access this area before due to a shortcut that needed unlocking.

Engage the boss, which consists of Vierra (4000 HP), Paul (3000 HP), and Shierra (2500 HP). Vierra and Paul are physical attackers, while Shierra is a magic attacker.

To defeat the bosses, buff your Physical Defense (PDEF) with Rudeus and focus on bursting down Shierra first.

If you are having trouble surviving, use Ruijerd to apply a Physical Attack (PATK) down debuff to Paul and Vierra. This, combined with Rudeus's DEF buff, will significantly reduce their damage.

After defeating Shierra, focus on taking down Vierra.

Once Vierra is defeated, you should be able to outheal Paul and finish him off.

Submit Quest 73 (and implicitly Quest 74) to complete the main game.