|The following information is from the Adventure Time comic book series.|
It may not be part of the same canon or continuity as the animated series.
Truth Field Projection Princess (aka "Mandatory Truthful Response Field Emitter And Polarity-Aligned Honesty Particle Atmospheric Wavefront Generator With Decoupled Quantum-Phased Linear Projection Matrix Princess") is a princess who speaks in standard Internet slang and 'l33t sp34k' with the power to emit energy fields that make people tell the truth. She helped Finn in his search for Ewlbo by helping him interrogate wizards. Like most other princesses, she has a crush on Finn.
In Issue 12, she helped Finn to figure out who Ewlbo was by using her truth field. She then used it on Finn to get him to tell what was the best way he wanted to smooch a princess, but he put his hand in his mouth so he couldn't talk. She was one of the princesses seen at the party at Issue 15.
She is green and has an orange dress. Her dress has a sleeveless top part which curves downwards in a V-like shape. Right above where it curves, the top section which is lighter in shade than the bottom and has a bold green line also in a V shape. There is a green oval gem at the top of her dress. It is right below a piece of fabric, with a green stripe on the bottom, which is draped over her shoulders and ends at her upper back. This outfit is similar to a sailor uniform. This top part is still connected to the long, orange bottom half. She wears long, yellow gloves that have a green section at the top. Her head is rather large, and she has a darker green line that circles around her head and ends at her eyes. Her crown is similar to Princess Beautiful's.
She can use her mind to make a green field that can make anyone tell the truth to whatever question she asks.