[1][2] Spinomantis phantasticus males measure 36–38 mm (1.4–1.5 in) in snout–vent length.

It is a very conspicuous species, presenting a distinct green-brown dorsal patterning and large spines all over the body.

[3] The male advertisement call is a sequence of 4 or 5 "metallic" double-click notes.

[3] Scpinomantis brunae occur along brooks in pristine forests at elevations of 500–1,200 m (1,600–3,900 ft) above sea level.

However, subsistence agriculture, timber extraction, charcoal manufacture, spread of invasive eucalyptus, livestock grazing, and expanding human settlements are threats to its habitat.