Before they've fully adjusted to the darkness, and are aware via anything but the feel of earth under their hooves that the path has sloped downward a little, it has given way under them, some of the flora and some distressingly large rocks along with it. Clarity can't even teleport. It's too dark to see where she might be going.
Joy happens to be the farthest one down the slope when it starts to go, and right next to one of those distressingly large rocks. Consequently, he is the first one off the edge of the unseen cliff below, and not conscious at the time.
Luckily for him, Brightblaze is second. She dives, gets herself under him - and finds out that dragons are heavy, even pony-sized ones, and she needs all four boots to achieve stable lift and get him safely to the ground. Which means not a hoof to spare to hang onto him, which means some very delicate balancing that's going to take time, which means she'd better hope Streak can take care of the three non-fliers by herself.
Clarity's next to tumble down the hill, yelping, trying to resist the urge to light her horn and see where she's going because that will just ruin everybody's vision -
"I don't have time to explain," she says as rapidly as she can, "but if you let go exactly when I say, you will reach the ground safely. Trust me?"
- solves mysteries, finds out facts - has no reason to want to harm her -
"Yes," she squeaks.
"Good. Now," she says, and lets go and spreads her wings and leaps to catch Guiding Star just as she hurtles over the edge, while beneath them the tree swings its stately way over to catch Clarity at just the right place and time to take her weight and hold it. The leafy branches are quite comfortable, certainly in comparison to just about anything else she could have hit.
Clarity falls. Clarity lands on the tree and hangs onto it for dear life.
"AAAH - oh hi - fancy seeing you here," says Guiding, laughing nervously, when caught.
She takes the extra second to poke her head up above the cliff edge and look for any trace of Cordy in the path of the landslide.
No such trace exists where she can see - but she can tell the path splits halfway up, around a harder shelf of rock. Logically, therefore, Cherry Cordial must have gone the other way. If she had been flattened in any visible area, there would be signs.
Down goes Streak to extract Clarity from her tree.
"Thank you," she says, shaking a little.
Being in less of a hurry this time around, she can carry Clarity down more sedately.
"Where's Cordial?" she asks when she's on the ground and has done a headcount. "Is Joy okay?"
"Cordial was carried a different way by the landslide," says Streak. "I don't know where she is exactly, but it's likely to be that way." She points in the appropriate direction.
"I think Joy's okay," says Blaze. "I hope Joy's okay." She pokes him with a tentative hoof.
"Here, I know a little healing magic, everypony close your eyes if you don't want to have to readjust to the darkness -" She bends over Joy, shuts her own eyes, and casts a spell good for blunt trauma.
"Hi. Better?" she asks, dimming her horn and opening her eyes. "You caught the landslide worst."
"Well, you do have scales. Okay, let's see if we can find Cordial, I guess - unless anyone else wants a healing spell?"