Guide:Defending against invasion events

Overview
This guide deals with the events currently implemented in version 1.2 of Terraria.

Blood Moons
Blood Moons are rather frequent events that can be a hassle for newer players who are caught unaware. Not only does the monster spawn rate increase dramatically during a Blood Moon, but the max amount of enemies that can be on screen also rises significantly, allowing swarms of enemies to appear at one time. Additionally, zombies can break open doors during this event, posing significant danger to NPCs inside houses. However, there are ways to profit from Blood Moons if one is prepared, especially thanks to rare spawns like The Groom.

Goblin Army
Goblins will appear at the spawn point and kill any NPCs they find. They will continually spawn until their army limit is reached before the event will end. This group has multiple types of units with different attack patterns, so strategies for dealing with them will differ depending on the type of goblin.

Solar Eclipse
The monsters spawned during a Solar Eclipse are very powerful. The Reaper acts similarly to a Wraith, but with higher stats. The Swamp Things are extremely fast, and they are as common as zombies. Vampires are equally as common as zombies, and can turn into bats if the player is above them. Eyezors are not very common during a Solar Eclipse, but they can shoot lasers from their eyes, making them formidable enimies. They are slightly faster than regular zombies. Frankensteins are common as zombies, but move much faster.

Frost Legion
There are three unique monsters in the Frost Legion, named Mister Stabby, Snowman Gangsta, and Snow Balla. The Frost Legion does not happen on it's own. The player has to craft a Snow Globe to summon them. They can be summoned with ingredients only in hardmode, but you can still defeat them in a non-hardmode world.

Pumpkin Moon
The enemies during a Pumpkin Moon are very dangerous, especially The Headless Horseman and Pumpking. The player has to craft a Pumpkin Moon Medallion to start a Pumpkin Moon.

Pirate Invasion
The Pirate Invasion is very similar to the Goblin Army, except the pirates are human. The Pirate Invasion has multiple types of units with different attack patterns.

Methods
Generally, Blood Moons can be seen safely through by simply holing up in your base, as long as all doors are either prevented from opening inwards or simply barracaded by blocks. Blood Moons do not spawn truly dangerous enemies; they simply increase the spawn rate and maximum onscreen limit while introducing a few rare variations such as Corrupt Bunnies and Corrupt Goldfish. This means that players who are adept at handling zombies and Demon Eyes have little to fear from this event, and can actually profit by it.

The Goblin Army's members do not specifically attempt to hunt down and kill NPCs; rather, that is just a side effect of them spawning near the player's starting point and attacking the player. If the player is strong enough to easily handle the goblins, a long, flat field near the base would be the best place to deal with the army, as it would be close enough to the spawn point to appear while keeping the goblins away from the NPCs. This assumes, of course, that the player is strong enough to deal with the swath of continually spawning goblins and willing to engage them in plain-old mano-a-goblin fighting. Check the article on the Goblin Army.It already has several methods for dealing with them.

The Solar Eclipse strategy is simple to understand. Every enemy but the Reapers and Vampires use standard Fighter AI, (and even the same jump range as basic Zombies and Goblins,) and will walk into pits just like any other zombie. Lava pit traps will destroy the whole invasion force but the reapers. Hence, the easiest way to nullify most of the threat is to dig a simple tunnel underneath a small lava pit on some leveled terrain. That allows players to simply focus on fighting the Reapers alone, (which are rare enough that you rarely fight more than one at a time,) while collecting all the drops. Check the article on the Solar Eclipse. It already has several methods for dealing with them.

For the Frost Legion,if you're far enough underground then the snowmen won't spawn, even after getting the message that they've arrived, so you don't have to head back to your house immediately upon receiving message of an imminent attack. However, they will remain and will appear if you surface. The Snowmen are incapable of jumping down from simple wooden platforms, meaning it is possible to construct a basic trench with a wooden platform above it, and be completely out of harms way. If you place lava pits on either side of your house, you can defeat most of the snowmen that spawn, however, Snow Ballas may block up the traps, inhibiting the trap from killing any more snowmen. Filling the empty space of any traps with Wooden Beams will prevent Snow Ballas from blocking up the traps. The beams occupy the same layer as other furniture and do not block movement.

For the Pumpkin Moon, since the wave number increases based on the number of enemies killed, taking a Battle Potion to increase the spawn rate is highly advised. If this is done, the player should bring two potions into battle, since one of them taken at the beginning of the night will wear off about halfway in. Most Pumpkin Moon enemies are susceptible to the Ichor Debuff, making a Flask of Ichor or the Golden Shower spell very valuable for this event.

For the Pirate Invasion, if you want to face the pirates head-on you must be prepared. Defeating these pirates is not an easy feat for a fresh hardmode player. You will want to use weapons that pierces multiple enemies at once, such as the Shadowbeam Staff or the Magical Harp. Alternatively, you can make sure the pirates stay below you, with you on a wooden platform. Then use some kind of high-level Spear to slay the attackers. When a captain attacks, focus all of your attention on him, because he will stop attacking when attacked. If you have the Uzi, Flamethrower, or Minishark/Megashark it is good to continually fly over the pirates and shoot at them as it is hard for them to shoot you down. Check the article on the Pirate Invasion. It already has several methods for dealing with them.

Lava
Lava is a useful tool to help thin out the numbers of enemies. Making shallow pools of lava is a common way to burn enemies to death while allowing their item drops to collect as they approach your home. Other variations include "waterfalls" of lava or even entire moats, albeit using large bodies of lava means any item drops will be destroyed as well, though it is always fun to watch zombies pour into a pit of lava en masse. It is possible to get the lava to a low enough depth that enemies are burnt but items are not, and can be tested by throwing a low value item (copper coins can be useful) into the pool, and seeing if it disappears.

Spiky Ball Trap Moat
Similar to the lava pool is the Spiky Ball Trap Moat. If you have recovered spiky ball traps from the Lihzahrd Dungeon, you may dig a moat completely under your house. The moat should be at least 12 blocks deep. Next, mount spiky ball traps to the underside of your house at regular intervals. Connect the spiky ball traps to a 3 second timer inside your house. Activate the timer once the invasion begins to rain down spiky balls on the Goblin Army.

Dart Trap
Although they do not deal a lot of damage, dart traps are an easy-to-use method of defending your base - all you have to do is set them up on the outside of your entrances and set up manual triggers using switches or levers, or automatic triggers such as pressure plates or timers. It's a good way to keep the weaker enemies out of your base, although it's more of an offensive technique than a defensive one. If you're using one of the aforementioned automatic techniques, you should be careful not to let you or your NPC villagers get shot when going out of their houses.

Active Stone Blocks and Actuators
If you have the mechanic its easy. Place the active stone block one side of the door and wire it to a switch and it block zombies and most goblins, or even make the "door" out of active blocks and turn them off when you need to go through. The same effect can be achieved with actuators.

Pit
Digging a pit on both sides of your base is a simple but effective way of holding back most of the goblins, save for sorcerer and archer goblins. The nice thing about pits when compared to the other methods is that you don't need any items found in midgame pre-hardmode like lava or finding the mechanic. Just simply dig a hole five deep by six wide or dig the pit next to a wall so when the goblins try to jump the pit they will hit the wall and fall into the pit. The downside to using a pit by itself, (without lava or other traps), is that after taking out the sorcerers and archers you still need to take care of the goblins in the pit. However, you can use the spikeballs dropped from the goblins you killed earlier and throw them into the pit to take them out from a safe distance.