Watcher currently in beta but coming soon to main branch of Slay the Spire. Some deck suggestions assuming you know what the cards do.
Guide to Watcher Archetype
Like Water Decks
Stay in calm stance to get free block from Like Water. Since you’re not going into wrath, you want non-attack damage, usually Pressure Points. Alpha(Omega) can work too. Scry is good in this deck to find your damaging cards or set up your block faster
Scry a lot to get free block from Nirvana. All the scry cards are good - Just Lucky, Third Eye, Foresight, and particularly Cut Through Fate since the draw can chain you into more scry cards
Stance Dance Decks
This is a powerful archetype that changes stances a lot - calm, wrath, and ‘exit stance’ cards are all good. You can get free block from Mental Fortress, recur Flurry of Blows, draw cards with Rushdown, as well as getting energy whenever leaving calm stance. You can also use Halt while in wrath to get extra block and then change out of wrath the same turn to avoid taking double damage
Wallop and Halt can give a lot of block while in wrath stance, potentially allowing you to stay in wrath during the enemy’s turn so you can keep dealing double damage next turn. However you might want a Tranquility as an emergency exit
This is a common archetype with a lot of ways to build it. The idea is to save up retain attacks until you can kill the enemy in one go. Battle Hymn, Sands of Time, Windmill Strike and Reach Heaven can be used for retain attacks. Then on the winning turn you can either enter wrath or divinity to multiply your damage (and this can be a retain card too like Crescendo, Blasphemy+ or Worship+). Establishment is useful but not mandatory. Spirit Shield is strong here because retain cards increase hand size
Talk to the Hand Decks
TTTH places a permanent debuff on an enemy that gives you block whenever you hit that enemy. The debuff is prevented by artifact, so you might want other debuffs (like Wave of the Hand) to clear artifact stacks before playing TTTH. Cards that can multi-hit enemies like Flying Sleeves and Ragnarok are good. Strange Spoon and Omniscience can help you get more copies of TTTH
Fasting is a powerful card if your deck is cheap enough to get around the drawback - Just Lucky is good because it benefits from both strength and dexterity. Or you can make up for the energy loss using Deva Form or energy relics. Conjure Blade is another card that benefits from energy. You can use Deus Ex Machina to get more energy
Small Mantra Decks
This is not a very common archetype where you can build up to divinity quickly using Prostrate / Pray and if your deck is small enough you can expect to have fairly consistent hands on divinity turns. Signature Move can be good
Use Omniscience to get Wish. Choosing the plated armor mode twice can make you hard to kill in some fights.