Nex attacks with all three combat styles but is limited to two per phase. She has a standard melee attack (the infobox lists a melee max hit of 27, while the strategy page describes it hitting "up to 30") and the wiki notes she "will always follow up with two additional melee attacks if her target remains within melee distance." Her basic auto-attacks hit even harder at range — the infobox lists a Ranged max hit of 60 (her shadow-phase shots) and a Magic max hit of 33 — which is why the correct overhead prayer per phase matters so much. Using the correct protection prayer reduces melee damage by 80% (66% in the final phase) and magic damage by 50% (66% during the blood phase). Each phase ends when you drop her to a health threshold and kill the matching corner mage.
Smoke phase (begins with "Fill my soul with smoke!"): Nex uses Smoke Rush, which can poison; this is the only phase where her basic magic does not drain prayer. Stand in melee range (melee distancing) and the targeted player flicks Protect from Melee, then switches to Protect from Magic when she changes target. Specials: Choke (infects the furthest player with the least magic defence and spreads to adjacent players — have one ranger act as a choke tank with a gas mask, facemask, or slayer helmet), Drag (pulls a player in and disables their prayer; less likely if Protect from Magic is on), and Smoke Dash ("There is... NO ESCAPE!" — darts down an aisle for up to 50 damage; dodge the direction she faces). Kill Fumus at 80% health (2,720 HP) — weakest to stab.
Shadow phase ("Darken my shadow!"): her shots are now Ranged, so pray Protect from Missiles to halve the damage. Damage rises the closer you are, so stand at maximum distance and attack from afar. Specials: Shadow Smash ("Fear the shadow!" — shadows under each player erupt for up to 50; move within three ticks) and Embrace Darkness ("Embrace darkness!" — standing next to Nex deals constant damage; back off until it clears). Use shadow resetting — stand under Nex to force her back to centre — and do not attack while resetting. Kill Umbra at 60% (2,040 HP) — weakest to ranged.
Blood phase ("Flood my lungs with blood!"): Blood Barrage heals Nex and drains prayer; pray Protect from Magic. Stand spread out in melee distance to avoid the 3x3 AoE splash. Specials: Blood Siphon ("A siphon will solve this!" — she summons up to eight Blood Reavers and kneels; all damage to her heals her, so stop hitting her and farm the reavers, which heal you for 50% of damage dealt to them) and Blood Sacrifice ("I demand a blood sacrifice!" — a marked player must move at least seven tiles away within ~4 seconds; the strategy page lists "up to 50 damage through Protect from Magic" that heals Nex and drains 33% prayer, while the infobox lists a Blood Sacrifice max hit of 80). Kill Cruor at 40% (1,360 HP) — weakest to slash.
Ice phase ("Infuse me with the power of ice!"): Ice Barrage freezes you for 15 ticks if you are not praying Protect from Magic and drains prayer. Specials: Containment ("Contain this!" — a 5x5 icicle burst for up to 60 damage that disables prayer; pray Protect from Missiles if trapped) and Ice Prison ("Die now, in a prison of ice!" — a 3x3 stalagmite cage that shatters after ~4 seconds for up to 75 damage unless a stalagmite is destroyed; free trapped players with stab or crush attacks, or a salamander). Kill Glacies at 20% (680 HP) — weakest to crush, but still range it.