《光晕》中的反派之一，洪魔的最高形式。

尸脑兽被假定为虫族形态的最高阶状态。只有当接近“临界质量”的虫族融合在一起的时候，这一点与原始尸脑兽很相似，但规模更大，尸脑兽才能形成。它通过一种未知的方式，有可能是心灵感应的方式，对整个虫族发号施令，并充当中心智库的角色。正因为如此，尸脑兽有可能保存着所有虫族的记忆，哪怕是那些包含了谜一般“起源”的独立的个体。尽管尸脑兽有引导整个虫族的力量，但似乎却不具备指挥虫族对抗小规模战斗的能力。原始尸脑兽是虫族野生阶段的最高级形态，也称智慧形态。作为虫族中少见的一种类型，原始尸脑兽与其它类型有很大差别，完全没有移动能力的它们显得十分被动。原始尸脑兽很像是由三种战斗形态融合在一起而构成的庞大的球状组织，外表还附有纺锤体状的外生结构与周围环境相粘附。

尸脑兽是虫族意识形态的化身，为了实现自身繁衍扩张的野心，它肆无忌惮的搜寻、吞噬着星系中一切智慧的生命体并操纵他们作为自己的傀儡。第一只尸脑兽，大概生存于 10 万年前，被光环的第一次启动所消灭。随后第二只尸脑兽形成，并躲藏于 Delta 光环中，它似乎非常了解先行者们的科技，甚至捕获了 2401 引导者忏悔切线，改装了光环上的心灵运输系统，并了解了光环的构造。这是一只不同寻常的尸脑兽。

从外形上来说，尸脑兽更像是捕蝇草：它是一个结实的带有触角的巨大实体，肥胖的颈部与模糊的脑袋，但其巨大的嘴却可以用很低沉的语调说话。它庞大的触手具有强大的力量，并有足够能力从光环深处扩展至表层上百公里的地方。

原始尸脑兽的寄主与其它战斗形态的寄主不同，它们都有特性使得其寄主在精神上能够对虫族的同化有一定的抵御，从而保有一定的原始意识形态。但是，虫族能够对原始寄主的记忆进行高度的详尽分析，过滤出每一条对虫族有用的信息，并把这种重要信息传递给整个虫族，而这些信息，被原始尸脑兽进一步整合，以制定它们的策略。当虫族需要执行高级任务，例如驾驶大型战舰、操作复杂机器的时候，就要首先建立原始尸脑兽。

原始尸脑兽在 HALO 系列中出现和描述过几次。第一次出现就是 HALO 1 中被虫族感染的凯斯舰长一关，由凯斯舰长和几名被感染的人类和精英战斗形态虫族所组成，虫族需要驾驶真理与和谐号战舰逃离光环；它后来被星盟的精英特种部队消灭（小说内容）。第二次出现是在 HALO 漫画小说，由工程师、野猪兽、人类战斗形态虫族和维修船上的其他动物所组成，准备驾驶维修船逃离，后来被半嘴精英 Rtas 'Vadumee 消灭。第三次出现是在 HALO 2 博爱之城一关，坠落的鹈鹕运输机驾驶舱可看到。第四次是在 HALO 3 虫族大门一关，虽然没有出现，但是驾驶坠落沃城的大型战舰只有原始尸脑兽才能完成。

尸脑兽是洪魔的一种形态，因而洪魔诞生就是尸脑兽诞生。

洪魔诞生也不得不说也是一种巧合，起因：先驱被自己视为淘汰品的先行者奇袭并驱离银河系后，愤怒之余，重新开启一个被搁置很久的计划，他们凭借自己强大的科技汇聚了至少12种未知生物（这其中也包括一名先驱），创造出了可怕的虫族-洪魔(Flood)，决定在银河系释放这种生物武器作为制裁手段向先行者复仇，并主导一场重估生命发展方向的试炼以判断他们认为能继承他们衣钵的种族——人类是否真的能继承衣钵。

先驱将这至少12种以未知生物为素体组成的虫族首领“上古尸脑兽 (Gravemind)” 放置于储存舱，投放在银河系边缘的一颗废弃行星上。它就是后来的永生者 (the Timeless One)，也叫做原基 (Primordial)，而尸脑兽的意识则来自那名融合为虫族的先驱个体，先行者称它为受囚者 (the Captive)。它的目的是要将先驱与先行者战争的真相告诉想要了解真相的人：衣钵的意义、虫族的起源、人类的角色、先行者不是衣钵的继承者、人类在通过测试之后可以继承衣钵。

在没有成为尸脑兽时，虫族的存在相当稳定，它们不会自动增生，但是会在感知生物体的附近形成，尤其是有自我意识及『内观能力 [?]』的生物体。

而在『野生』阶段时，虫族只能利用『费洛蒙』通讯来进行本体的协调，研究指出，它们传递的信息必定无法太复杂。这些个体能够取得宿主的能力和记忆，一旦虫族建立出尸脑兽后，便会进入『互助』阶段，也就从这时候开始，虫族的危险性会暴增。远距不同形态群组的同步化，以及个体间的职业专门化，将不再藉由费洛蒙通讯来进行。因为群组对形势变化的反应，就战略层面而言算是瞬间或近乎瞬间完成的，期间完全不会因为距离而有任何的『时间延迟』。根据推论，虫族在后野生阶段拥有某种『心灵感应 [?]』形态，不过尚未获得证实。

尸脑兽，与其前身原始尸脑兽相似，是虫族超级细胞 (FSC) 及宿主复杂的神经系统的融合体。尸脑兽对自身所创造的机动体的控制能力，就像是一般个体控制自己的四肢一样。因此，在野生阶段时，尸脑兽的控制还局限于个体层面，不过一旦进入互助阶段，便会由中央复合智慧发号施令。

虽然并没有任何严谨的试验资料，不过根据实际情报显示，如果将机动体从尸脑兽中移除，便会回复到野生阶段。至于某个尸脑兽的机动体是否会受其他尸脑兽的影响，并没有充分资料可供推论，不过逻辑上应该有可能。尽管如此，由于尸脑兽所有个体均极为相似，且目标都一致，所以几乎无法找出它们当中的区别。

The squad exits the brig and are immediately attacked by the guards on the mid level.

The team levitates up to the mid level and frees the second group of Marines, who armed themselves, again, with dropped Covenant weapons.

The team returns to the highest floor and kill the reinforcements.

The Marines, one by one, step into the lift and leaves the area.

If the player stalls:

士官长 enters the lift and is sent to a room with Marines waiting. The dead Honor Guard Ultra Elite seen earlier still lies on the ground.

Three Elites run out of a nearby door, pursued by a lance of Drones. The team eliminates them and enters through the open door. They continue into a hallway, walk pass another dead Honor Guard Ultra lying on the floor, and encounter a pair of Honor Guard Elites fighting some Brutes and another lance of Drones. After all the Covenant are dead, another swarm of Drones emerge from the door and attack the team. The team eliminates them and continues to the next hallway.

The team enters another corridor, and sees a pair of Brutes and some Jackals attacking a few Honor Guard Elites. They eliminate them and continues onwards, walking past a dead Hunter as they leave the area. They enter another area, guarded by a pair of Hunters, who are eliminated by the team soon.

The door in front of the team opens, revealing a duel between an Energy Sword-wielding Honor Guard Elite and a Brute on a platform on top floor of the first Valley of Tears. Eliminating the two as well as the Jackal Snipers in the distance, the team continues downwards, meeting more Elites fighting a Brute under a Deployable lookout tower. Drones fly down and attack another pair of Hunters on the lower floor, but are soon intercepted by a pair of Elite Rangers. The team hikes up and finds a door, guarded by a single Brute. They eliminate it and exit the Valley. Behind the door reveals a wide and long staircase, splattered with purple blood. They walk down the slope.

The teams exits and finds a Gravity conveyor. They step into it and begin to convey to the other side. A slipspace rupture opens on their far left, and UNSC In Amber Clad emerges from it.

The In Amber Clad flies by overhead.

The team reaches the other side as the sound of In Amber Clad crashing is heard.

A pair of Grunts and a pair of Elites turns by the corner and attacks the team. A Brute appears and fires at the Elites. The team eliminates the Covenant troops and reaches the first Hanging Gardens. Intense fighting between Honor Guard Brutes and Minor Elites rages over it. The team eliminates the troops and a pair of Elite Rangers emerges from the tower. After clearing the area, the team continues and encounters another Gravity conveyor. Elites and Grunts emerge, and begin to fire at the pair of Jackals led by two Brutes on the other side, who moves to the side the Covenant Separatists are on. The team eliminates all the Covenant and enters another door. Drones fly by the narrow corridor, unaware of the Human presence.

Continuing down the corridor, the team arrives at a small area with a Gravity Lift in the middle of it and plants on the lower level. Drones and Elite Rangers fly in the narrow space, firing at each other. Elite Honor Guards and Special Operation Elites provide support fire, but are soon intercepted by a pair of Brutes and two Jackals. The team clears the area and advances into another narrow corridor. Walking out the door, reveals another Gravity Conveyor.

They move on to the other side, reaching the second Hanging Gardens. Grunts run around it, attacked by a pair of berserk Brutes. The team continues to the next Gravity Conveyor, and enters a door. Now on the bottom of another wide and long staircase, the UNSC forces are attacked by a few Brutes. Moving up as they eliminates the Brute, they reach the door at the top and arrives at the second Valley of Tears. An Elite defends itself from a Brute and a Jackal Sniper, while another Brute attacks a pair of Grunts near the pond below. The opposite door opens, and three Elites, one of them an Honor Guard, along with with a Fuel Rod Gun-wielding Heavy Grunt, who proceeds to fire at the UNSC forces. Scaling the Valley, the team hikes up a slope, meeting two Energy Sword-wielding camouflaged figures, followed by several Special Operations Grunts. After eliminating the troops, the team enters another door and finds an Elite as well as several Grunts patrolling the area.

They continue into the Mid Tower, meeting more patrolling Elites and Grunts, who are all Special Operation units, if not Ultras. After being spotted, Brutes and Jackals enter the room, joining the firefight; the team eliminates the patrols and opens the next door. They find a long bridge leading to the Mausoleum of the Arbiter. In the middle of it are Elites fighting Brutes, Jackals and Drones for control of the bridge.

The team continues, but are intercepted by more Covenant Separatists, including a pair of Hunters. The surviving forces enter the Mausoleum and come across a very large fight inside.

After the room is cleared:

科塔娜's avatar appears on a pedestal next to the exit.

The exit opens, with several cloaked Elites and a sword-wielding Honor Guard Councilor running out. 士官长 kills them and continues through the bridge.

{Cutscene}

塔塔罗斯和他的鬼面兽带着凯斯、{Johnson}和模板:343GuiltySpark toward a platform where the 模板:ProphetsofTruth和怜悯先知 wait for them, with three Phantoms.

Three Brutes do so rather brutishly. Keyes notices 琥珀号 in the tower before being pushed into the Phantom. The two Phantoms take off. 塔塔罗斯 kneels before the Prophets.

真相先知 hands 塔塔罗斯 the Index.

Infection Forms spring up and rush them. The Brutes spot them and they get ready. The Brute Honor Guards throw their pikes aside and stomp on several of them. 塔塔罗斯 flattens one with the Fist of Rukt. The Brutes manage to shoot or crush most of them, but one gets through and lodges itself to Mercy's throat, knocking him off his throne.

怜悯先知: (screams in agony)

塔塔罗斯 reaches to remove the Infection Form.

塔塔罗斯 turns to Truth in surprise.

真相先知：（对怜悯先知）“朝圣之旅可不等人，兄弟……即使你也如此。”

真相先知 boards the Phantom and the Honor Guard Brutes follow immediately, but 塔塔罗斯 hesitates at the dying 怜悯先知. He looks at the Index, makes his decision, and turns away from 怜悯先知.

关卡结束