I personally like your multiple branching stories idea, but prefer more of what Knee had come up with (excluding myself here for obvious reasons)
Great Cliffside
Shimmering Ice Caverns (I like the stones idea)
Frosty Peak
Centiskorch
Darmanitan
Carkol
Job 40:
Ice Cavern Ruins
Deep in the heart of the Icy Mountain, lies Regice's chamber. The area is a massive round chamber, with the ceiling being covered in icicles and the floor being covered by ice. 4 massive pillars stand at the corners of the room. At the end of the room lies Regice's statue. In order to unlock it, the automatic activation system comes on, and the player must succeed in a memory game. After a few rounds with some enemies to defeat in between, Regice awakens. Regice refuses to help the group at first out of fear of angering Regigigas, and thus attacks the group, intending to bring them to it in exchange for not being destroyed, thus forcing the group into battle.
Regice
Like Regirock, Regice has several attack patterns. Note as well, the floor is ice, which causes the player's movement to be hindered, think Mario ice physics. Regice can slide along it perfectly fine. All of Regice's ice moves can potentially freeze the player.
Pattern 1:
Regice jumps to the side of the arena, and uses Ice Beam, creating a large path of ice. Regice will spin along said path, and use Icicle Spear. The Icicles will scatter about, with red circles indicating their landing area. Regice will then jump to the center for a few seconds.
Last Quarter Version: Regice will now create more Icicles, and the path will be slightly higher on elevation, making it so only special attackers can hit it.
Pattern 2:
Regice uses Stomp, causing some of the Icicles on the ceiling to crash down from above. Red circles indicate their landing position. Regice will stay in the center as they are falling.
Last Quarter Version: Regice will instead use Earthquake, creating a shock wave around it when it slams the ground. More icicles will fall than before.
Pattern 3:
Regice will stand in the center and use Ice Beam, with Lock-On indicating where it will land. It will slide to a different area after each Ice Beam, but will not move too far. Regice will then move to the center and spin around, creating a Blizzard around it. Which it will send around the arena. The player must stand behind one of the pillars to avoid the attack.
Last Quarter Version: Regice's Blizzard will now come out slightly faster than before. After usage, it will randomize the player's position in the room.
Pattern 4:
Regice uses it's ice to generate weaker copies of itself, which will move towards the player and attack with Ice Punch. These copies are far weaker than Regice and will go down to a few hits. If the player does not deal with all them in time and then make it to Regice, Regice will unleash a powerful Focus Blast at the player which cannot be avoided. If the player hits Regice as it prepares to use it, Focus Blast will cancel out and Regice will jump over to another position in the room.
Last Quarter Version: Regice will generate more copies. The copies can now use Ice Shard as a long range weapon. Regice also now requires multiple hits to stop it unleashing Focus Blast.
Pattern 5:
Regice will slide towards the player by charging towards them with Ice Punch, unlike it's weaker clones which did not slide. Regice will do this a few times, with Lock-On indicating where it will go. Regice will then jump back to the center.
Last Quarter Version: Regice can also use Power Up Punch, which while going a shorter distance, does more damage than Ice Punch and boosts Regice's damage for a short time.
After taking 3/4 of it's health, Regice's attacks grow more difficult and more powerful, aka the Last Quarter Versions.
Upon defeat, Regice threatens to explode like Regirock did, but Pikachu talks to it and mentions how Regigigas is destroying the land and threatens to destroy everything if left unchecked, and also says they got Regieleki and Regirock on their side. Regice realizes that supporting Regigigas would benefit no one, and thus agrees to help them if they can find the next titan. It points them in the direction of the next chamber as everyone leaves.
Job 41:
Togekiss
View attachment 338257
Togekiss is a Flying/Fairy Pokemon introduced in Generation IV. The final evolved form of the iconic Togepi, Togekiss is known for it's power in battles. In this game, Togekiss is a well rounded Pokemon stat wise. It has solid Defenses, mediocre attack, and average speed. It's stats are well rounded, allowing it to adapt to situations as needed. It's signature skill is Metronome, which allows it to call upon certain attacks from the other playable Pokemon. It can be quite unpredictable, as it could call upon very good or very bad moves for the situation. Togekiss in short is an adaptable Pokemon, being a wild card in any given situation, allowing it to fit in nearly anywhere so long as things go well.
Job 42:
Honchkrow
View attachment 338259
Honchkrow as an Elite Pokemon is fairly unique in that it mainly summons Pokemon to do it's dirty work. It mainly summons droves of Murkrow to attack foes for it, preferring to stay back and fly above where the player can reach them. After defeating a few groups of Murkrow, it will become angered and use Brave Bird, rushing at the player. If dodged, the player gets ample time to attack Honchkrow, but it will fly away after taking a few hits. It will then repeat the process until it is knocked out.
Murkrow
View attachment 338260
Murkrow act as flyer enemies summoned by Honchkrow. They will attempt to use Peck when close to a player, as well as Aerial Ace for a stronger move. If far enough away, they'll use Dark Pulse, which can potentially flinch the player. Other than that, they are rather weak, with their strength being in numbers more than anything. They will stop spawning once Honchkrow is knocked out.