The Mathura school of art flourished around Mathura (Uttar Pradesh) during the Kushan period (1st–3rd century CE). It was an indigenous, home-grown style that evolved from the earlier Indian tradition of carving Yakshas and Yakshis (folk nature-spirits). The early Mathura Buddha images are modelled directly on the robust, fleshy, smiling Yaksha figures, giving them a distinctly native character.

It also used spotted red sandstone (from the Sikri quarries) and showed the Buddha with a shaven head, a benevolent expression and minimal, thin drapery — features that grew out of Indian conventions rather than foreign ones. So its best characterisation is indigenous features with a Yaksha influence.

The other options describe different things: Hellenistic (Greek) drapery and naturalistic realism belong to the Gandhara school of the north-west, not Mathura. "Sandstone and floral arches" mixes a material with an architectural feature that is not the defining trait of this sculptural school, and "predominantly wooden monastery design" does not describe the Mathura stone-sculpture tradition at all.

Hence, the correct answer is indigenous features with Yaksha influence.