Age of Sigmar/Tactics/Old/Order/Devoted of Sigmar

Warscrolls

Heroes

• Witch Hunter: Not too dangerous, unless you send him at Wizards or Daemons. Funnily enough, the rule doesn't specify CHAOS Daemons, so your Witch Hunter will have a field day with Seraphon, as ALL his attacks doing D3 damage actually makes this guy pretty dangerous.
• War Altar of Sigmar: Surprisingly very dangerous at range, especially against Chaos and even more against Chaos Daemons. It is also immensely good at buffing your units and keeping them safe. One Altar in your army can also have Volkmar the Grim chilling in it, who makes the thing even better. Do keep in mind that, as it gets damaged, it will have trouble keeping up with your Knights, so an all-cav list may not be the right place for it.
• Warrior Priest: Never ever give this guy the Greathammer as its stat block was obviously written by someone who didn't get the rules (Both choices are even on save 3+, Warhammer is better for everything above, although only marginally). Other than that, they are decent though not impressive in melee and have some very nice prayers up their sleeves and most importantly, unlike most Priests, they aren't that squishy. In fact, with a shield, they are decidedly non-squishy and not just by Empire standards, either.
• Excelsior Warpriest: The only toy for this faction specifically released for Age of Sigmar and is basically just a normal war priest with a single hammer. He has a prayer that can heal d3 wounds on an order unit or do the revers to a chaos unit (this drops to one wound if the unit is non-chaos). Also allows a gryph hound to be set up but this takes away the battleline designation from your flagellants.

Troops

• Flagellants: Bad hit rolls and no saves make for a very unimpressive unit at first glance, but if you get a War Altar or a Hurricanum (or better both) close to them, you have an absolutely terrifying unit that nobody wants to get charged by, because even if your opponent kills them, they can deal unpleasant damage to him.

Battalions

Pilgrimage of Wrath

A War Altar of Sigmar, 2 Warrior Priests, a Witch Hunter and two units of Flagellants

Army Building

Have the option to build cheap effective hordes that can be buffed to the max by war altars/priests. Removing battleshock within 10" of a war alatar has its pros and cons as it negates the fleeing flagellants dishing out mortal wounds on a 4+. Witch hunters are just plain bad, even against daemon wizards they don't have the save or range to be worth what you're paying for an enemy. The excelsior warpriests sole advantage over the run of the mill warpriest is the ability to pray an arcane bolt and heal units as opposed to models. As they cost the same points it's really your call. The army works based around prayers to Sigmar as well as your priests and war altars unbinding spells all day.

Allied Armies

FREE PEOPLE or STORMCAST ETERNALS are the best choices.

External links

Rules are here

https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/aos-warscroll-witch-hunter-en.pdf

https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/aos-warscroll-war-altar-sigmar-en.pdf

https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/aos-warscroll-warrior-priest-en.pdf

https://www.games-workshop.com/resources/PDF/AoS_Warscrolls/aos-warscroll-flagellants-en.pdf

Age of Sigmar Tactics Articles
General Tactics	Tactics Realm Of Battle Malign Sorcery Path to Glory Skirmish
Order	Cities of Sigmar Daughters of Khaine Fyreslayers Idoneth Deepkin Kharadron Overlords Lumineth Realm-Lords Seraphon Stormcast Eternals Sylvaneth
Chaos	Beasts Of Chaos Blades of Khorne Disciples of Tzeentch Hedonites of Slaanesh Maggotkin of Nurgle Skaven Slaves to Darkness
Death	Flesh-Eater Courts Nighthaunt Ossiarch Bonereapers Soulblight Gravelords
Destruction	Gloomspite Gitz Ogor Mawtribes Orruk Warclans Sons of Behemat
Others	Monstrous Arcanum Legends Old Rules