The Legiones are the strongest unit in the Monastery of Ascension, each requiring one of their own respective Ascension keystone needed to kill them once each time. They are hunted for their signets which are in turn used to create the expensive ascension crossbow and its off-hand counterpart; the signets have an uncommon drop rate, confirmed to be 1/50.
Level 95 Slayer is required to enter the Legiones' chambers. It is not required for fighting them. This requirement can also be boosted.
The Legiones use fairly inaccurate magic attacks, and are able to summon lightning strikes on the floor that can be avoided, similar to the Corporeal Beast's area-of-effect magic attack. Legios always use two lightning attacks, then a basic magic attack (with the exception of Secundus and Sextus).
These lightning strikes are not to be underestimated; they can deal incredibly high damage based on the player's position, and always hit with 100% accuracy regardless of the player's armour rating. If on the rims of the lightning strike, the player will only be hit for one hit of roughly 1400+ base damage. Standing one step away from the center will deal roughly 1800-2000 base damage, while standing exactly in the center will deal 2200-2400 base damage. Apart from the increased damage, the rate of damage also increases the closer the player is to the center; when standing exactly on top of the lightning strike, damage incurred is twice as fast compared to the edges.
Unlike most monsters, protection prayers/curses will not reduce the damage of the lightning attacks by 50%; instead, it takes a smaller amount (roughly 200-300 damage).
The pattern of the lightning can be somewhat controlled: the Legio will use one lightning strike on the players current spot and the second on the first place the player clicked from their current standing spot. As such, if the player clicks on one spot and then detours to another, the lighting attacks can be completely avoided.
The Legiones have no weaknesses; however, because Ascension creatures benefit from heavy melee and magic defensive bonuses, Ranged is the only way to kill them efficiently.
High level ranged armour is advised when fighting the Legiones as this will near-negate their regular magic attack. Power armour is especially useful due to increased damage dealt which will significantly speed up kills; tank armour simply increases your durability against their lightning attacks. Pernix equipment is a good choice when fighting the Legiones, as you get some health and damage boost when wearing it.
Food is more of a priority than prayer, as prayer does not have much of an effect on the orb lightning attack (except when combined with Devotion) so bring more food than potions. Beast of burdens are recommended over other familiars due to being able to bring more food, especially for Tertius and Quintus who have mechanics which can eat up a lot of food for the inexperienced. Experienced players will not need to bring beast of burdens, and can settle with an offensive familiar (Shadow nihil or Steel titan), and bring little food due to Soul Split's healing effect is enough to nullify damage from their standard attacks.
Instead of a Farsight sniper necklace and Soul Split, Protect from Magic along with Rigour can be used in combination with an Amulet of zealots for faster kills and slower prayer drain overall (compared to using Soul Split and ranged turmoil. However, this will require more food if the player is hit too much from their lightning attacks.
Players should engage the Legiones using the hit-and-run tactic - where they attack the Legiones while they keep running around, which will make them avoid the lightning orb attacks most of the time and help conserve food. Each Legio has their own unique special attack which will activate when they reach 75%, 50% and 25% life points. Despite this, the hit-and-run tactic should still be used as normal, except for Legio Quartus and Legio Quintus (see their respective sections below).
Soul Split should be the primary overhead curse; if this is not applicable, then Protect/Deflect Magic should be used as the second priority. Avoid the lightning orb attacks as much as possible for every Legio; Rapid Fire and Unload will hold the player in place until they manually cancel it, which can subject them to prolonged lightning exposure which can result in severe damage or death. Snipe also has the same issue as Rapid Fire and Unload, though wearing Nightmare gauntlets will make using Snipe feasible.
When fighting the Legiones, it should be noted that they enjoy a damage reduction the further away a player is from them. Being under them when the attack is calculated will deal full damage, although this is not viable due to their small size. It is recommended to unleash thresholds/ultimates while the player is next or near them in order to maximise damage inflicted. Always watch the Legiones' health, as damage is capped at quarter intervals, so if Legio Primus has 15,532 life points and Shadow Tendrils are used against him, it will only deal up to 533 damage, while the player will take damage to half of what the actual hit will be, wasting adrenaline and food. Bleeds or low damaging abilities should be used near quarter intervals so the more powerful abilities can be used once that interval is breached.
The preferred action bar setup:
With good experience and high-leveled weaponry, one can expect to kill the Legiones in 20-40 seconds.
Each Legio has his own unique ability which intensifies or is performed again when they reach 75%, 50% and 25% life points respectively.
Legio Primus' unique ability is that the lower life points he has, the more damage he will deal - akin to that of Dharok the Wretched. For every 25% life points that Primus loses, his lightning orb attacks gain 200 extra damage (so at 25% life points, being in the centre of his lightning will deal 2900-3000 damage twice per tick for two ticks). Using the hit-and-run tactic as normal nullifies this ability, however it is best to eat up as being caught in the middle of a lightning attack can cause massive damage.
Legio Secundus' unique ability is using the lightning orb attack more frequently as his life points lower. At 75% health, he will use three orb attacks, then one basic magic attack. At 50%, he uses a simple magic attack every four orbs, and at 25% he will exclusively attack with lightning. This is generally not a problem as using the hit-and-run tactic as normal will nullify this ability, however the lightning orbs will be more frequent so having high life points is advantageous when most of his are depleted.
Legio Tertius' unique ability is summoning Monastery of Ascension units when his health lowers - 3 Rorarii when he reaches 75% life points, 1 Gladius when he reaches 50% life points and 1 Capsarius when he reaches 25% life points. With fast reactions, it is possible to kill Tertius before the Capsarius is able to heal him, though one should not expect for this to happen most of the time. Once Tertius is killed, his reinforcements will die with him if they are not killed yet.
One should be extremely careful when dealing with the Capsarius. If one kills it too fast while it is healing an injured Ascension member (in this case, it will most likely heal Tertius), it is possible for the Caspsarius' defence buff to permanently apply to whatever it was healing. If it was healing Tertius while this bug occurs, Tertius will be near-invincible, taking very little damage from your attacks. If this happens, kill off the minions before dealing with him.
It should be noted that the Ascended called by Tertius will spawn under him. Players should be careful if they use Bombardment or Corruption Shot, as the AoE damage will hit the Gladius and most likely cause it to surge towards the player and stun them, leaving them open to the orb attacks. Freedom and/or Anticipate should be used when Tertius summons the Gladius, then attack it from afar to cause it to dash to the player. This will leave them free to use Bombardment and Corruption Shot without having the Gladius stunning them.
Any remaining minions after Tertius is killed with die off as of the 29 June 2015 update.
Legio Quartus' unique ability is teleporting the player next to him when he reaches 75%, 50% and 25% life points and launching an additional lightning attack at/around the spot he teleported the player, on top of his regular attacks. This act can be seen as both a benefit or threat - if the player is very far from Quartus, being teleported nearby should not have much of an effect to their life points. However, being nearby may cause the player to be stuck for a few ticks inside an orb attack, proving dangerous to be in so as soon as the player is teleported (it is easy to predict if they watch his health bar) to immediately run away before the orb attack hits them.
Note: It may take multiple clicks to move away from Quartus as the teleport cancels your action in doing so when using Revolution to fight.
Legio Quintus' unique ability is summoning "Lines of Ascension" in the laboratory when he reaches 75%, 50% and 25% life points. This is very dangerous and makes Quintus possibly the most tedious to fight for inexperienced players as death is a much higher possibility due to limiting the player's space to avoid orb attacks, in addition to dealing much more damage than them. The first and third lines he summons will run horizontally, while the second line runs vertically.
It is worth noting that the player can "force" the lines to spawn as when he reaches 75%, 50% and 25% life points respectively, a line will spawn wherever the player is currently. Doing this near the edges of the laboratory will effectively nullify them if they perform the hit-and-run tactic while keeping away from them completely.
It should also be noted that the lines will only hit once per tile, meaning that if you step on an affected tile and do not move, you will only be hit once. However, unless using Protect/Deflect Magic with Devotion, this is unfeasible because of the lightning attacks will force the player to move out of the way immediately. Running over a line will deal very heavy damage (more then the lightning attacks), so it is advised to leave a very large area unaffected by the lines for inexperienced players. These lines act much like the Queen Black Dragon's fire walls, so experienced players can completely avoid damage by standing next to a line and running over it (this will not work if two lines are parallel to each other).
Legio Sextus' unique ability is a longer lasting and larger radius lightning orb attack that occurs with a lowered amount of life points. He also does not use the regular magic attack unlike the other Legio. This should be kept in mind while running around; doing so in an erratic way is not advised as the larger radius and prolonged duration will probably end up killing the player. An aggressive familiar can be used to distract Sextus, as with the other Legiones, they will attack with their regular attacks rather than lightning. However, multiple pouches may be required as he can hit very hard and often against them. Despite this, Sextus is generally straightforward to kill, like Primus.