Here's my set-up when dealing with steel watchers on Balanced:

I found the Steel Watchers to be weak against Thunder/Lightning/Reverberation attacks.

I place my characters on four corners away from one another. This is so when the steel watchers detonate, your characters do not get hit all at the same time.

I put Chain Lightning, Lightning, Shatter, Witch Bolt on Gale. Make the ground wet or icy. This causes more damage. There's a wearable item that grants you reverberation on attacks (can't remember where it's from), and this causes the steel watchers to detonate/self-implode.
I have Shadowheart as Tempest Domain Cleric. I put Shatter (thunder damage), Sleet Storm and Lightning on her. It's important to put the sleet storm around the mobile steel watchers, because they will walk around and if you can make them fall or prone, this gives your characters time to run/put distance between you and the enemy
On Astarion, he normally does melee damage for me, but for this fight you can equip him with Thunder and Lightning arrows. You can also use his turn to throw water.
For your Tav character, I had Circle of Land Druid because she also had Sleet Storm, Call Lightning, and can tank as owlbear. If the Steel Watcher is already standing on ice, use Crushing Flight as owlbear and land on them to knock them prone. This again, gives your other characters a chance to attack. Another spellcaster-type similar to Gale would help too.

For me the key was to do ranged spells/attacks, and don't get caught standing too close to them when they detonate. Bring Misty Step scrolls if your characters don't have this ability, to quickly get out of the blast zone.

Last edited by Lillith; 20/11/23 05:32 PM.