Mastons were large predators native to Sentimenous Virgo. They generally weighed around one hundred twenty kilogrammes and were around two hundred ten centimetres tall. Mastons were large and hairy and had powerful tails. They could easily overpower a human. They weren't especially intelligent.
A sexually aroused Maston secreted an airborne toxin which paralysed any animal lifeform in its immediate vicinity. The exact range of this effect is unknown. This is speculated to be an evolutionary adaptation designed to ensure that an exhausted post-coitus Maston would not have to look too far in order to find its next meal. (PROSE: Slipback)
The Mastons were driven to extinction millions of years ago when their planet was destroyed. The computer of the Vipod Mor brought a Maston forwards in time to attract a Time Lord and to distract the crew. (AUDIO: Slipback)