I'm of the belief that Alexandrite is specifically the fusion of a Garnet, an Amethyst, and a Pearl. Meaning that if Amethyst, Pearl, Ruby, and Sapphire, or in this case, Opal, Ruby, and Sapphire fused, then the result out not be an Alexandrite. However, I know this theory is not well liked, so I'll keep it to myself. You can't deny that the weapon choice and mind set would be different though.

When the Crystal Gems started seeing the tremors going through the water, they, as well as Jasper, assumed naturally that the Cluster had begun to take form sooner than they had anticipated, as minor quakes were one of the signs meant to indicate its taking of form. The drill was ready thankfully, and they could go whenever they wanted, but Steven stopped them when they made a beeline for the machine. His mental powers, the ones he still had the least control over, had started acting up in his sleep again. And this time, he'd seen a fusion they'd all forgotten about recently, rising out of the ocean.

"Aventurine?" Opal questioned. "That's what Lapis and Peridot are calling themselves," Steven said, "Or maybe their minds are actually working as one now.. I don't know. But she's back! She's by the communication hub. Peridot's still holding her back, but I don't think she can keep it up much longer." Opal nodded, "Stay here with Jasper and the drill, we'll handle this. Gems, to the warp pad!"

Opal, Ruby, and Sapphire ran off towards the warp pad, teleporting to the communication hub. When they arrived, they saw that Steven had been right; Aventurine was above water, chains of liquid metal still binding her as her liquid metal wings tried desperately to break her free. "Maybe I can hit Lapis's gem from here if I hurry." Opal said, reaching to summon her bow.

Sapphire stopped her, "No, if you attempt that, the odds of actually successfully hitting Lapis's gem without damaging Peridot are slim to none. More likely, you miss and your arrows help free her. You know what we have to do." Opal sighed, "You're right. Haven't had to use her in years." "You don't mean.." Ruby's eyes widened as Opal nodded, "We're putting an end to this, and we need Alexandrite to do it."

Opal reached out with all four hands, two for Ruby, two for Sapphire, and began to dance with them both, her flexible nature letting her match the both of them at once. They began to glow, merging together and growing large, creating the massive gem Alexandrite. She was less than a head lower than the entire height of the tower she was standing next to, making her several dozen times larger than Aventurine.

As they formed, the chains finally broke, freeing the twisted fusion. "Finally.. I wasn't expecting you to last this long, I'm impressed." She said to herself. "Aventurine!" Alexandrite roared from the second jaw beneath her face. "What? No, I- stop! Weak.. we've been holding us back too long. I think it's time we have some fun." Aventurine turned to Alexandrite, flying at roughly eye level with the four gem fusion.

"We're only giving you one warning. We don't have to fight. You're outnumbered." Alexandrite said. Aventurine grinned cruelly, "I may be outnumber," Her hands moved, the water rising behind her in a massive wave that didn't crash, remaining still behind her like a cannon ready to fire, "But you're outclassed. I can't way to break you gems apart!" She threw her hands forward, and the tidal wave surged forward.

Alexandrite summoned Fire Opal's morning star, a burning strike countering the wall of water. As she turned to look for Aventurine, the metal making up the communication hub began to move, reaching out and wrapping around Alexandrite, chains and bars forming to hold her in place as Aventurine sent a storm of water, now frozen into ice shards, raining down on her.

Alexandrite grit both sets of teeth in pain before the lower jaw opened up and a blast of fire spewed out, melting the ice and engulfing Aventurine. She flew fast, avoiding too much damage, but was unfocused long enough for Alexandrite to free herself from the metal of the tower; which she promptly tore from the ground and flew at the liquid metal fusion in anger.

Aventurine caught it with her powers, prying it apart and changing the shape of the various metal chunks. What before had been a single solid tower was now a storm of drills fling at Alexandrite. She summoned Sapphire's shades and Opal's bow, focusing her future sight to avoid the drills and shoot the ones she couldn't out of the way. When the drill storm passed, she put the shades and bow together to create Snow Opal's crossbow, firing at Aventurine.

Fast as Aventurine was, she couldn't outrun future vision, and was hit by an ice arrow. She crashed to the ground in a chunk of ice, which she promptly melted, only to be punched into the ground by Garnet's gauntlets. Aventurine stumbled, dazed and in pain for a moment as gauntlets appeared on all six of Alexandrite's hands, all six of them throwing off sparks with the amount of electricity they were throwing off.

The ground shook with the force of Alexandrite's repeated strikes to the ground, every hit felt all the way back at the barn, and each impact discharging lightning through Aventurine. And still, when Alexandrite had to stop to breathe, Aventurine flew up. She was hurt, but it didn't seem like there was much that could separate the two gems. Their bitterness, despite coming from different sources, and to some extent being aimed at each other, was keeping them on the same wavelength mentally, making the fusion incredibly powerful.

"Like Fire Opal, but about a hundred times worse." Alexandrite muttered to herself as a wall of water and steel rose on either side of her, both walls solidifying before flying at her to crush her. Alexandrite held out all six arms, and still only barely managed to stop the walls from meeting. Both of them began melting, enveloping the large fusion and lifting her into the air before flying down hard and crashing into the ground.

"Sorry, but there's only room enough for one abomination on this planet," Aventurine said, another metal drill forming above Alexandrite, this one massive and spilling as it was launched at her, "But thank you for opening my eyes about fusion." She added mockingly. Fire Opal's morning star saved her, crashing into the drill with enough force to send it careening in the other direction, and not losing any momentum, letting it continue to spin and hit Aventurine in the same motion, flinging her into the air.

The morning star vanished, Alexandrite summoning Opal's bow, Ruby's gauntlet, and Sapphire's shades. She brought the three weapons together, the result being a massive trebuchet. Aventurine spread her wings and righted herself, only to see a large ball of energy rocketing towards her. "You two should spend some time apart." Were the last words Aventurine head before the ball hit her, blasting Lapis and Peridot apart.

Alexandrite caught them both, lowering them to the ground before poofing. Opal, Ruby, and Sapphire landed on the beach with their every nerve and muscle screaming, and the desire to simply retreat into their gems for healing overwhelming. Unfortunately they wouldn't get the chance, as the island that had once housed the communication hub now shook violently. They hadn't noticed it during the battle due to their size, but the quakes had continued even after Aventurine had freed herself. Jasper had been right; the Cluster was forming.