Evil religious background

This background offers mainly front-row guilds that combine melee and spellcasting.

Reavers

RoleMelee, focused on offense
DescriptionGuild thematically built around destruction. Has fairly good melee offskills, as well as WIS-based blasts. Training most skills is locked behind their energy bar - the good skills require getting to the 3rd layer. If you have no energy, reincarnating into the guild can take a while, as you need to build it up to be able to train many skills.
WeaponsPolearms, axes
Important skillsReaver strike, Way of the scythe
Important spellsWord of spite, Word of blasting
Rep/questsKilling mobs gives destructive energy that allows training better skills. Using word of spite improves damage against mobs of that race. A variety of quests, generally focused on destroying various things, gives some bonuses.
Other considerationsReincing into the guild takes a while if you have no energy. If you do not use any offensive reaver skill for a couple days, you start losing energy. As such, this guild isn't very suitable if you plan to play infrequently.
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Tigers

RoleMelee, focused on offense
DescriptionTigers are a bit of an oddity - they are an assassin guild in a PvE-oriented game (although at the time of writing this, their assassination missions are disabled). Similar to monks, they are a martial arts guild, but in addition offer the Tiger claw spell, whose stunning effect is useful in experience parties. They also get lock picking and stealth skills.
WeaponsMartial arts
Important skillsDim mak
Important spellsTiger claw
Rep/quests(TODO: info here)
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Disciples of Chaos

RoleMelee, focused on offense
DescriptionDisciples are a 10-level guild that allows you to transform into a chaotic spawn, which gives a fairly good attack, improves stats, and adds tentacles that do damage and can wear rings. The guild is not meant to be taken as a stand-alone one,
WeaponsDepends on the chosen followup guild.
Important skillsChaotic spawn, Clawed strike, Choreography of mutilation
Rep/questsKilling mobs in spawned form improves the spawn, increasing stat bonuses and tentacle count.
Other considerationsExperience gain is reduced substantially while in spawn form. This is a base pre-requisite guild for Tzarakk, Kharim, Nergal, and Aelena. If you do not plan to join one of those, joining disciples is generally not recommended.
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Tzarakk

RoleMounted melee
DescriptionMelee guild that mainly focuses on evolving a chaos mount. Very effective for new players, but doesn't scale as well as others.
WeaponsPolearms
Important skillsRampage, Charge/Trample, Riding/Combat riding, Mastery of mounted combat
Important spellsSteed of Tzarakk
Rep/questsKilling mobs makes the mount stronger. Collecting trophies from outworld mobs allows you to train some skills higher.
Other considerationsYou can only join one of Tzarakk/Kharim/Nergal/Aelena.
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Kharim

RoleMelee, focused on defense and offense
Description 
WeaponsLong blades, shields
Important skillsManner of lordliness, Situational warfare, Scourge of dark steel
Rep/questsCollecting keys needed to train some skills. Can gather souls from mobs and use them in various ways. Can create and evolve a chaos blade.
Other considerationsYou can only join one of Tzarakk/Kharim/Nergal/Aelena. Kharim can't cast spells in combat. Also available in Nomad background.
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Nergal

RoleMinion-based, no clear focus
DescriptionMinion-based guild that focuses on gathering and training various minions, pokemon-style. Minions can fight in melee, tank instead of you, or blast from backrow (all this works even if you solo). The guild doesn't offer any fighting skills beyond what Disciples give. A very versatile guild, but not suitable for newer players, as it requires a lot of game knowledge.
Important skillsCast chaos, Embrace the gifts
Important spellsParasitic swarm, Harvest vitae, Reap potentia, Enthralling parasite, Mind siphon, Nourish enthralled, Awake enthralled
Rep/questsThree usage-based skills (Conduit of the hive, Immunology, Morphology) that improve various guild features. Each minion has its own levels and spells and needs to be trained separately. Complete missions to get evolution points to enhance minions or your stats. Completing chaotic acts gives some bonuses.
Other considerationsYou can only join one of Tzarakk/Kharim/Nergal/Aelena.
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Aelena

RoleMelee, focused on offense and support
DescriptionFocused on collecting and using poisons. Poisons can do damage, reduce resists and avoid, interrupt spells, and more. Generally considered weaker than other tank guilds. Dexterity is their most important stat.
WeaponsShort blades
Important skillsWound
Important spellsSting of aelena
Rep/questsUsing sting of aelena eventually allows getting more poisons.
Other considerationsYou can only join one of Tzarakk/Kharim/Nergal/Aelena. The guild isn't as good as other tank guilds - especially lack of Parry is a significant drawback. Also available in Civilized background.
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Spiders

RoleSupport
DescriptionSpiders are a secondary guild, focusing around summoning a spider demon that can enhance various stats, hpmax, spells, etc. It does not work well as an only guild, and is not suitable for newer players.
Important skillsCasting skills/masteries
Important spellsAll demon-manipulating spells
Rep/questsNo
Other considerationsGetting usable demons requires expensive sacrifices, and luck.
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Evil Priests

RoleBlaster
DescriptionBack-row blaster guild, its main advantage is that its harming spells cannot be resisted (although some mobs are immune anyway). The disadvantages are that the spell has a rather poor spellcost/benefit ratio, the guild offers nothing else and gets boring fast.
Important skillsCast harm, Mastery of pain
Important spellsHarm body, Aura of hate
Rep/questsAffinity to Burglefloogah improves harming spells (TODO details?), fervor is a momentum mechanics that improves some spells.
Other considerationsIt is common to take some priest levels for healing spells, aura of hate, and cardiac stimulation. Full priests are rare, however.
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