How do I design a base that is safe from the Old One's Army in Terraria?

Designing a base that is safe from the Old One's Army in Terraria requires careful planning, strategic building, and understanding the event's mechanics. The Old One's Army is a wave-based event where you must defend the Eternia Crystal from enemies that spawn from portals on either side of the arena. The event is triggered by placing an Eternia Crystal Stand and using an Eternia Crystal, which can be purchased from the Tavernkeep NPC. To create a base that can withstand this event, you need to focus on defense, mobility, and resource management.

First, let's discuss the mechanics of the Old One's Army. The event consists of multiple waves, with each wave increasing in difficulty. Enemies will spawn from portals on both sides of the arena and will attempt to reach the Eternia Crystal. If the crystal is destroyed, the event ends in failure. The event is divided into tiers based on your progression in the game: Tier 1 is available pre-Hardmode, Tier 2 is available after defeating at least one mechanical boss, and Tier 3 is available after defeating Plantera. Each tier introduces stronger enemies and more challenging waves.

To design a base that can handle the Old One's Army, you need to create a fortified arena with multiple layers of defense. Start by choosing a flat area or flattening the terrain yourself. The arena should be at least 100 blocks wide to give you enough space to maneuver and set up defenses. Place the Eternia Crystal Stand in the center of the arena, and build walls or barriers around it to protect it from direct attacks. However, make sure the barriers are not too close to the crystal, as some enemies can attack through walls.

Next, set up platforms at different heights to allow for vertical movement. Platforms are essential for dodging enemy attacks and reaching flying enemies. Space the platforms about 10-15 blocks apart to give yourself enough room to jump and move around. You can also add ropes or teleporters for quick movement across the arena.

For defense, consider using traps and sentries. Traps like spear traps, flame traps, and spiky ball traps can be placed along the ground to damage enemies as they approach. Sentries, which are summoned using sentry weapons from the Tavernkeep, can provide additional firepower. Place sentries strategically around the arena to cover all angles of attack. You can also use lava moats or dart traps to slow down and damage enemies.

Lighting is another important consideration. Ensure the arena is well-lit to make it easier to see enemies and navigate the area. Use torches, lanterns, or other light sources to illuminate the arena.

Resource management is crucial for surviving the Old One's Army. Make sure you have plenty of healing potions, mana potions, and buff potions. Buffs like Ironskin, Regeneration, and Swiftness can significantly improve your survivability and combat effectiveness. Additionally, stock up on ammunition if you're using ranged weapons or mana-restoring items if you're using magic.

Class and equipment considerations are also important. Each class has its strengths and weaknesses in the Old One's Army event. Melee classes can tank damage and deal high close-range damage, but they may struggle with flying enemies. Ranged classes can deal consistent damage from a distance but may need to manage ammunition. Magic classes can deal high burst damage but may run out of mana quickly. Summoner classes can rely on minions to deal damage but may need to focus on dodging attacks. Choose a class that suits your playstyle and equip the best gear available for your progression tier.

Common mistakes to avoid include not preparing enough defenses, underestimating the difficulty of higher tiers, and not managing resources effectively. Make sure to test your arena before starting the event to ensure everything is set up correctly. Additionally, avoid placing the Eternia Crystal Stand too close to the edges of the arena, as this can make it harder to defend.

Advanced techniques include using teleporters to quickly move between different parts of the arena, setting up automated traps using wiring, and using environmental hazards like boulders or explosives to deal massive damage to enemies. You can also optimize your arena by using blocks that slow down enemies, such as honey or slime blocks, to give yourself more time to react.

In summary, designing a base that is safe from the Old One's Army requires a combination of strategic building, resource management, and understanding the event's mechanics. By creating a fortified arena with multiple layers of defense, setting up platforms for mobility, and using traps and sentries, you can increase your chances of successfully defending the Eternia Crystal. Remember to prepare adequately, choose the right class and equipment, and avoid common mistakes to ensure your base can withstand the onslaught of the Old One's Army.