Guide:Astrum Deus strategies

Astrum Deus is a late Hardmode boss that can be fought after the Lunatic Cultist in order to gain access to Astral Ore. Astrum Deus is summoned by using a Titan Heart on an Astral Beacon at night. For future battles after the first defeat, Astrum Deus may be summoned using a Starcore on an Astral Beacon at night instead.

This guide will mention items exclusive to Expert and Revengeance Mode with no special formatting and will follow the intended progression.

Terrain Preparation
Astrum Deus is not bound to any biome and will not enrage due to biome restrictions. As Astrum Deus requires a lot of space, it is important to cover up holes in the ground to prevent yourself from getting caught by uneven terrain. Generally a large open space with several platforms is adequate.

For a dedicated arena, flatten out the surface of a biome (or an area that's about 800 to 1000 blocks long). It is suggested to line the floor of the arena with Ice Blocks because you have significantly higher acceleration on it. You'll need 3,000+ platforms for this, so get those first. Place four layers of platforms, each spaced at least fifty blocks apart from the nearest block/platform. This will give you plenty of vertical and horizontal space to fight the boss.

Additionally, killing a few of the Celestial Pillars will minimize interruptions during the fight.

Armor

 * Hydrothermic armor are generally the preferred choice for almost all classes.
 * Additional options include Beetle armor for Melee players, Spectre armor for Mage players, and Plague Reaper armor for Ranged players.
 * Reaver armor is extraordinarily powerful for Mage players when paired with the Eidolon Staff.

Accessories

 * Wings are a near necessity. The preferred wings are Exodus Wings or the MOAB.
 * Angel Treads are extremely useful for boosting flight time and keeping distance from Astrum Deus.
 * The Heart of the Elements is a great option that gives a sizable jump boost as well as summoning the elementals for extra DPS.
 * Asgard's Valor or Statis' Ninja Belt provide a dash that helps increase horizontal mobility.
 * Asgard's Valor provides defensive boosts such as knockback immunity whereas Statis' Ninja Belt provides rogue and mobility boosts such as a longer dash, extra jump speed, and the effects of Master Ninja Gear.
 * The Celestial Jewel and Ursa Sergeant help minimize the impact of the Astral Infection debuff.
 * Alternatively, the Margarita drink will halve its duration at the cost of some defense and life regeneration.
 * Melee players using yoyos should equip a Yoyo Bag to increase the range and effectiveness of the yoyo.
 * Magic players can make use of the Sigil of Calamitas and/or Mana Flower along with Mana Potions to recover their mana during the fight.
 * Mana Regeneration Potions can be vital as it allows mana to regen quickly even when the player is moving.
 * Summoners can boost their minion count and damage with the Statis' Blessing and Statis' Curse.

Weapons
Weapons made from the Lunar Fragments are typically your best options.

Melee

 * The Aegis Blade is an extremely good true melee weapon that can decimate Astrum Deus. However, it can be very hard to obtain due to it being a legendary weapon.
 * The Ultimus Cleaver is a slightly weaker option that deals extreme damage to the boss and is significantly easier to obtain.
 * The Grand Guardian performs phenomenally with large explosions on every hit.
 * The Tenebreus Tides performs very well due to its high damage and piercing.
 * The Solar Eruption's piercing will do high damage against Astrum Deus, especially when hitting many worms at once. However, its low range can make it risky to use.
 * The Brimlash Buster is a strong weapon that can hit many worm segments at once allowing for high damage.
 * The Entropic Claymore is a powerful sword that can deal high piercing damage with its homing plasma balls.
 * The True Forbidden Oathblade, while being of a lower tier, has high damage that can mitigate Astrum Deus' defense.

Ranged

 * The Scorpio performs phenomenally with alternate fire with a massive area of effect. Its homing capabilities make the fight very straight-forward as well.
 * The God's Bellows performs very well for the boss' first phase with its high piercing allowing it to deal significant damage to many segments at once. Though, this weapon falls a bit off at the boss' second phase due to the shorter and faster worms, especially when they're not often grouped together.
 * The Aerial Bane is an excellent weapon with its bonus damage to aerial targets.
 * The Charged Dart Blaster performs well, particularly with the alternate fire, enabling it to hit many targets at once.
 * The Shroomer has excellent damage, which helps to bypass the high defense and damage reduction of the worms.
 * The Vortex Beater performs well with a homing explosive and reasonably high base damage.
 * The Vortexpopper deals high damage, and if paired with Chlorophyte Bullets, will rarely miss a shot, allowing the player to focus on dodging Deus’s attacks.
 * Acid Rounds or Hyperius Bullets are the preferred ammunition for guns, while Rocket IIIs should be utilized with Launchers.
 * The Gauss Rifle works very well together with Plague Reaper armor, plus Adrenaline if the player is playing on Revengeance Mode or higher.

Mage

 * The Eidolon Staff is a powerful option that can hit many targets at once.
 * The Tome of Fates is similar to the Solar Eruption. It has good damage at the cost of being quite dangerously close to the worms.
 * The Razorblade Typhoon can tear Astrum Deus apart swiftly.
 * The Lazhar is a high damage option with strong piercing allowing it to melt the boss.
 * The Nano Purge is a good option that can deal with the high defense and damage reduction of Astrum Deus.
 * The Cosmic Rainbow is a powerful option that can be awkward to use but does well as the worms are falling back to the ground.

Summoner

 * The Stardust Dragon Staff is the best option for summoners, as it can pierce the many segments of Astrum Deus, especially when combined with the elementals from the Heart of the Elements.
 * The Spikecrag Staff is an excellent option with its wide area of effect being able to take advantage of Astrum Deus' large hitboxes.

Rogue

 * Star of Destruction can pierce the boss if used properly, and should definitely be utilised.
 * Cranium Smasher is a great option for Rogue users with good piercing and DPS.
 * Plaguenades are an amazing option for its high damage explosion and piercing, especially when paired with the Plague Hive.
 * Like the melee variants, the rogue variants of the Subduction Slicer and Fallen Paladin's Hammer perform very well as well.

Miscellaneous

 * The Well Fed buff provides a useful all around stat boost.
 * Farming the Blood Moon for Blood Orbs is a great way to gather potions for the fight.

Phase 1
Upon being summoned, Astrum Deus will take little damage until a few seconds have passed. Astrum Deus has 3 different attacks in this phase:


 * Fires lasers from each segment of its body, one by one.
 * Leaves behind astral mines where it initially traveled.
 * Attempts to ram into the player.

The lasers can be dodged by constantly maneuvering around Astrum Deus, while the mines released should be kept at a distance or have their placements memorized to help with staying away from them. Astrum Deus's rams may be avoided by simply jumping or dashing out of the way, however it should be noted that the boss' projectiles may occasionally get in the way, whether it be left over mines or lasers directly fired afterwards.

Phase 2
Once Astrum Deus is below 50% of its health, it will split in half and the fight will be composed of 2 worms. This is the most difficult section of the fight, as while each worm still goes with the original worm's AI, both of them act seperately and are considerably faster, meaning it is much more difficult to avoid attacks from one worm without being intercepted by the other. It should be noted however, that only one of the worms needs to be killed to end the fight entirely, so attacks should be focused on only one worm if possible. Phase 1 measures to avoid attacks still work in this phase, although dashing is notably riskier for avoiding rams from either worm.

General Tips

 * Disabling backgrounds can help players who have trouble focusing on all the different things that are going on during the fight.
 * In Revengeance mode and higher, using Adrenaline or Rage can remove a large chunk of Astrum Deus' health when it is low to swiftly end the fight.
 * Using the Overlay Minimap and changing its transparency with and  keys can provide the player with icon of bosses that are too far to see without the Minimap, making it a useful tactic to aim at bosses.
 * Using the Rod of Discord can allow a quick escape, especially if you are walled by several mines.