Devilline has dull teal skin, fluffy white and dark pine green hair, and four eyes with cyan irises and black pupils. She has a thin build with a small chest, a small torso, and relatively wide hips. Her gemstones are embedded in her sternum.
She wore a deep V-neck forest green bodysuit with a cyan star-shaped shawl that covered her neck. Her leggings were short and dark pine green. She wore dark pine boots with downward facing arrow cutouts at the tops.
She wore a sleeveless tri-colored deep V-neck bodysuit with a dark cyan top in the shape of a downward-facing arrow. Underneath was a lighter dark cyan section of the same shape. Her leggings were white and split off into black-cyan boots with a thin lighter dark cyan border. She wore black-cyan elbow-length armbands.
GemCrust describes Devilline as mischievous and devious, being the combination of Ice's shy and anxious personality with Heliodor's happy-go-lucky but cynical nature. Devilline deliberately does things to cause trouble and chaos. When formed, Devilline refuses to split. However, after a while, Ice and Heliodor eventually get tired of each other and split.
Devilline is unstable in a sense, but she loves herself and loves being herself. She doesn't believe herself to be a fusion of two Gems but just one; this is actually a touchy subject for her. Ice or Heliodor shouldn't be brought up around her or she will snap.
Heliodor makes Devilline unstable, her attraction to Ice is what makes Devilline not want to split, so she'll hold her constitute Gems hostage if she has to. She seems to get more unstable each time they fuse into her and it becomes harder and harder to separate.
Devilline likes to look as normal as possible, only showing her top pair of eyes when angered or frustrated.
As of Heliodor becoming a Crystal Gem, Devilline is much more stable now.
During the events of "I Am My Mom", Ice was spending some time with Heliodor, fused as Devilline. Once she sensed Alexandrite being formed, which peeked her interest, she rushed over, saw Aquamarine's ship leaving and went after it.
She became conflicted due to her components' own interests, and it's a wonder she didn't fall apart mid-flight. Ice wanted to rescue Steven and go back to Earth, but Heliodor wanted to go to Homeworld with Ice and stay there, so Devilline got irritated because she couldn't focus. However, she was brought down by the Gem Destabilizer.
Devilline possesses standard Gem abilities, bubbling, shapeshifting, fusion, regeneration, agelessness, and superhuman strength/durability.