Act IV is short and dense: five areas in about five minutes, from the Outer Steppes to the Chaos Sanctuary, ending with 
Diablo. Izual comes early, and the three seal bosses arrive within half a minute of each other at the end.
- Length
- 5+ min
- Areas
- 5
- Timed events
- 11
- Boss
- Diablo
The route
Areas change on a clock, not by where you walk: the act moves you through them in this order.
Act IV areas
| Name | From | Until |
|---|---|---|
Outer Steppes | 0:00 | 1:00 |
Plains of Despair | 1:00 | 2:00 |
City of the Damned | 2:00 | 3:00 |
River of Flame | 3:00 | 4:00 |
Chaos Sanctuary | 4:00 | the boss |
On the clock
Named monsters, rings and swarms arrive at set times, whatever area you are in. Times are minutes into the act.
| Time | Event | Who | Note |
|---|---|---|---|
| 0:30 | Ring of monsters | 24 ×  Cliff Lurker | |
| 1:10 | Unique |  Izual | The act's early unique, at 1:10. |
| 1:45 | Ring of monsters | 28 ×  Doom Knight | Two rings of Doom Knights, at 1:45 and 5:40. |
| 2:20 | Swarm | 22 ×  Dark Familiar | |
| 2:45 | Ring of monsters | 24 ×  Damned | |
| 3:20 | Super unique |  Hephasto The Armorer | |
| 3:45 | Ring of monsters | 12 ×  Urdar | |
| 4:32 | Super unique |  Infector of Souls | First of the three seal bosses; Lord De Seis and the Grand Vizier follow within 30 seconds. |
| 4:46 | Super unique |  Lord De Seis | |
| 5:00 | Super unique |  Grand Vizier of Chaos | |
| 5:40 | Ring of monsters | 30 × Doom Knight | Two rings of Doom Knights, at 1:45 and 5:40. |
| End | Act boss | Diablo |
Tips
- Act IV's demon lords breathe Inferno, which is all fire: fire resistance cuts it.
- Oblivion Knights cast Bone Spirit and poison skulls: their homing spirits follow you.
- Venom Lords appear in three of the act's five areas.
The boss
Diablo breathes fire and fires lightning, and his Bone Prison closes a ring of bone round you. Fire and lightning resistance carry this fight; keep moving so the prison doesn't pin you.
Named monsters
Super uniques in Act IV
| Name | Arrives | Modifiers | Minions | |
|---|---|---|---|---|
Hephasto The Armorer | 3:20 | Spectral Hit, Aura Enchanted | — | |
Infector of Souls | 4:32 | Extra Fast, Spectral Hit | 9 | |
Lord De Seis | 4:46 | Extra Strong, Aura Enchanted | 5 | |
Grand Vizier of Chaos | 5:00 | Extra Strong, Fire Enchanted | 9 | |
Darkwing | — | Extra Strong, Cursed | 7 | |
Riftwraith the Cannibal | — | Cold Enchanted, Teleportation | 8 | |
Taintbreeder | — | Extra Fast | 6 | |
The Tormentor | — | Magic Resistant, Fire Enchanted | 5 |
