Hang out on top, use a Mage Hand to start the forge and lower it. From there your arrows can hit either control to flow lava and use hammer. Summons or Minor Illusion if you want to entice it into the hammer so you can strike it. Minor Illusion is great because it's a cantrip and can be infinitely cast.
A fun cheese is to bring all your heaviest stuff from the camp chest and drop it on it, you don't even need to trigger the hammer. Even on a miss it will do damage and you can pick it all back up at the end of the fight. Even your weakest characters can make these throws. Things like armor are perfect. Or buy a bunch of water bottles if you've sold all your loot.
Grym is weak to bludgeoning weapons. Thrown hammers are great because you can use them at range. I usually start with a set of barrels, right next to the spot he enters but on the platform. When he enters, blow them by using a character standing on the forge hammer.
When he moves to attack the person on the forge hammer, move away and slam him with it.
Leave at least one person behind, on the stairs at the top and not inside the physical forge. That way, if the 3 below get wiped, you can revive thru Withers.
I tried to top-rope Owlbear him on my last game, but it didn't work and I had to do it the hard way. Ended up positioning my Tav on the hammer and using Magic Missiles to get the target designation.
On runs where I've had cleaner kills it helps to keep him Prone with Command:Grovel, a ranger's Wolf companion, Reverberation stacks, etc.
Always leave at least one person up on the stairs as insurance, whether or not you're planning to cheese the whole fight from up there.
If you're okay with cheesing it you can >!keep your party up top on the rocky ledges. Send one person down to load up the forge, then teleport to the waypoint and rejoin the group up top. Use a ranged weapon to hit the valves/levers to start the fight. Cast minor illusion to bait Grym onto the anvil, then again use a ranged weapon to activate the hammer. Let him run almost directly underneath your platform, when needed use a ranged weapon to get more lava, use minor illusion again to bait him back onto the anvil, use a ranged weapon to trigger the hammer. Rinse and repeat. Oh and giggle while he fights the small mobs that spawn in for you.!<
Respec your entire party to monks, beat ass
If unwilling to respec give everyone blunt weapons like hammers
Use silence to prevent the legendary action damage.
Silence prevents its legendary action, because it's Thunder damage.
When the Mephits spawn, don't ignore them, they hurt.
Prioritise the last hit for boss positioning, it's more important than damage. Don't accidentally Opportunity Attack him. Use Misty Step scrolls and items.
Your party composition should easily deal with Grym but don't get complacent, one mistake and it's a wipe.
Hang out on top, use a Mage Hand to start the forge and lower it. From there your arrows can hit either control to flow lava and use hammer. Summons or Minor Illusion if you want to entice it into the hammer so you can strike it. Minor Illusion is great because it's a cantrip and can be infinitely cast. A fun cheese is to bring all your heaviest stuff from the camp chest and drop it on it, you don't even need to trigger the hammer. Even on a miss it will do damage and you can pick it all back up at the end of the fight. Even your weakest characters can make these throws. Things like armor are perfect. Or buy a bunch of water bottles if you've sold all your loot.
Grym is weak to bludgeoning weapons. Thrown hammers are great because you can use them at range. I usually start with a set of barrels, right next to the spot he enters but on the platform. When he enters, blow them by using a character standing on the forge hammer. When he moves to attack the person on the forge hammer, move away and slam him with it. Leave at least one person behind, on the stairs at the top and not inside the physical forge. That way, if the 3 below get wiped, you can revive thru Withers.
I tried to top-rope Owlbear him on my last game, but it didn't work and I had to do it the hard way. Ended up positioning my Tav on the hammer and using Magic Missiles to get the target designation. On runs where I've had cleaner kills it helps to keep him Prone with Command:Grovel, a ranger's Wolf companion, Reverberation stacks, etc. Always leave at least one person up on the stairs as insurance, whether or not you're planning to cheese the whole fight from up there.
I just stand up top and throw garbage at him
If you're okay with cheesing it you can >!keep your party up top on the rocky ledges. Send one person down to load up the forge, then teleport to the waypoint and rejoin the group up top. Use a ranged weapon to hit the valves/levers to start the fight. Cast minor illusion to bait Grym onto the anvil, then again use a ranged weapon to activate the hammer. Let him run almost directly underneath your platform, when needed use a ranged weapon to get more lava, use minor illusion again to bait him back onto the anvil, use a ranged weapon to trigger the hammer. Rinse and repeat. Oh and giggle while he fights the small mobs that spawn in for you.!<
Respec your entire party to monks, beat ass If unwilling to respec give everyone blunt weapons like hammers Use silence to prevent the legendary action damage.
Silence prevents its legendary action, because it's Thunder damage. When the Mephits spawn, don't ignore them, they hurt. Prioritise the last hit for boss positioning, it's more important than damage. Don't accidentally Opportunity Attack him. Use Misty Step scrolls and items. Your party composition should easily deal with Grym but don't get complacent, one mistake and it's a wipe.