K'un Lun Konudrum
Return to the Dragon Cave temple and have Iron Fist do his thing.
Enter the temple.
The camera helpfully points out a smashable panel. Smash it to glimpse a dragon, then get caught in a falling tower. You'll need to match a quicktime prompt to leap to safety.
As Ms Marvel, shrink down and climb the spider thread.
There's a purple stud along the ledge left, but your mission path leads rightward, through all the spider junk. Once you finish falling, use the junk to build a Marvel platform.
Use this to smash the undoubtedly-ancient-and-sacred shrine, and build the pieces into a tightrope handle for Spiderman.
Cross over, and proceed down the rickety planks until they collapse. Smash the items here for some tiles.
Break through the cracked door, and push out the ornate mirror from inside.
Head to the center of the room and destroy some ninjas.
Have Danny charge up the central dragon shrine to send a beam off the mirror you just placed, into a pile of fireworks.
Build the pieces there into another mirror, and turn the push handle to get it in position (it will stop moving once you do).
Follow the beam to another little building. Shoot down the pieces roped to the ceiling.
These let you build a final turning mirror, which opens the cave door and leads to boss fight.
His fight skills are nothing special, just smack him around the room with Ms Marvel.
While you're smacking, you might keep an eye out for the five green-pots-in-straw around the room.
Two are on the left side of the room, two on the right side, and one down by entrance.
Getting all five is worth a minikit.
After Serpent takes about one-third damage he'll send a fire-tornado after you. Run from it, but you can still land a smack or two on him as you pass by.
Continue the sequence. A few extra goons will join the fight from time to time, but with Kamala's pummeling radius, you'll scarcely notice they're there.
When Serpent is felled, you'll switch to Danny. Use his charge button to ford the flames and reclaim the heart.
This completes the mission.