The Calamity Strikes mission is where things really start to get serious in Hyrule Warriors: Age of Calamity. It's the hardest level in the game by far up to this point, so make sure to merge weapons and have your character AT LEAST leveled up to 38.
It's a battle reminiscent of when Link makes his way through Hyrule Castle in The Legend of Zelda: Breath of the Wild. Veterans of that game will recognize the castle's grand banquet halls and staircases.
Help King Rhoam
The first objective is to help King Rhoam. Here's a handy map.
Link will reach an area with two Black Moblins. They're difficult enemies but can be wiped out with well-timed dodges and counter-attacks.
An Old Foe is back
You knew it was going to happen eventually. Guardians are all over the mission. Luckily, they're not as difficult to defeat as they are in BOTW, but they pack a mean punch and still track you.
The homing laser in particular is a real nuisance because it has a blast radius that will damage you if you don't dodge at the right time. Time it right before they fire to make sure you're out of harm's way.
Get used to seeing guardians because there are a LOT of them. You'll face three more as you make your way into the castle. If you chop off a guardian's legs, it'll switch to laser attacks. Besides dodging, you also have the option of using your shield with Y at just the right moment.
After you take care of the three guardians, a waypoint for a secret passage appears, taking you under the castle.
You'll face two more guardians as you make your way through the castle. Next comes an alert that guardians are at the dock, blocking any chance of escape. Now it's time to fight your way through some inner outposts, with a large Moblin and a Guardian Scout to contend with as well.
The scout is thankfully slightly easier to defeat, just use the same tactics that work on his bigger cousin.
When you reach the great banquet hall you'll meet another Ice Wizzrobe followed by another outpost before the party reaches the grand hall.
Here you'll run into one of the hardest enemies in the game – the White-Maned Lynel. He has a larger health meter than a regular Lynel and a radius fire attack to watch out for if you get too close. Fortunately, you can usually strafe around him to avoid his attacks and get a Flurry Attack opening.
Once you dispatch the Lynel it's time to make a run for it, as Guardians begin in from all sides. Sadly, King Rhoam's time is up. Well, until he comes back in BOTW. Congratulations on one more level in the books.