Sapphire

"Look what I found in Emerald's hammer collection, darlings. Such a shame it's going to be...splattered...with your remains."

Sapphire is a female contestant on Object Land Reloaded, but appeared way earlier in episode 2 of Object Land as a judge.

Personality
Sapphire is shown to be kind but sometimes moody. She speaks a strong English. However, as shown in Back From the Deader, Sapphire can also be crude, sadistic, and violent, showing she killed Lollipop, Yo-Yo, Lipstick, and Buttoney with one of Emerald's hammers.

Musical Mayhem!
Alongside Sunstone, Sapphire first appeared in "Musical Mayhem!" as a judge for the challenge. She gives Team Purple's music video a nine, but Team Lollipop's video a ten. She was not seen for the rest of the original series.

Back From the Dead
Sapphire returns as a contestant for Object Land Reloaded. Her face does appear in one of the portraits hanging on the wall of a room in Sunstone's building.

Sapphire appears inside of the box on the right, holding a Sunstone tea cup. She misinterprets herself to be the co-host of Object Land Reloaded, but Emerald corrects her. Since Toilet Paper, the original leader of Team Purple, was eliminated, Sapphire was put onto Team Purple as the leader of the team. She wasn't okay with it, but since she and Sunstone signed contacts (what she thought were just a fanfiction Emerald wanted autographed), she couldn't leave.

Back From the Deader
Sapphire tries to explain her plan, but then Swabby interrupts her. This episode showed of her more vicious side. She appears from above while Buttoney and Yo-Yo were playing "I Spy." She is holding a hammer from Emerald's collection of hammers, and threats to kill the round duo. After Yo-Yo and Buttoney bump into Lollipop and Lipstick, Sapphire finally has them cornered, making her able to kill the four.

One "eternity" after Gumball dies, Sapphire throws a rock at the renaming six Team Lollipop contestants, scoring Team Purple the win.

Bio
"Sapphire is a close, old friend of Emerald. She's an english gemstone who's apparently a sapphire from the crown jewels. The gemstone community love her movies and she has a large fan-base. Sapphire is a kind gem but can be a bit moody sometimes, and she's very private."

Trivia

 * The evil side Sapphire shows off in "Back From the Deader" could be a possible reference to Flippy from Happy Tree Friends.