The appearance of dragonewts varies by gender.
Dragonewt males don’t look much different than lizardmen. Their dark-green color changes to dark-purple. They sprout dragon wings and horns, and are covered by dense scales which act as a multi-layer barrier.
The women on the other hand, have a rather beautiful human appearance. Furthermore, they can also cover themselves with dragon scales, sprout wings and horns at will.
Gabil's squad of 100 developed the ability to transform into dragons for a limited time. The power of this form is noteable as Gabil was confident that each one could fell an imperial airship, Rimuru himself considers the Tempest's strongest force. However the drawbacks hit hard and if they don't go berserk they'll still become incapacitated for two days following the use of this form.
They gained this skill from Demon Lord Rimuru's Harvest Festival, allowing them to get closer to their draconic roots.