|Large map to show exact spawn location within Shatter Scar Vale.|
Previously to Patch 5.1 it seems that these guys mostly spawned after server restarts (see older comments on Wowhead and Warcraft Pets). However, there were cases of these guys being sighted and captured at other times (see post at press '5' to capture). More recent comments, since the patch, have indicate that these guys arent necessarily spawning after resets now. I had previously discussed, with my boyf, the possibility that Blizz have fixed these guys so that they now spawn from the remains of the larger infernals as the tool tip suggests.
Anyway, I set about casually killing some of the larger infernals. I killed 3 or 4, mounted up and did a lap of the area. I was at the ridge and there was another player mounted to my right. I saw the green paw on my mini-map, moused over it and it was a minfernal. The person to my right started to fly towards it and I followed. I have no idea why by this person hovered above the minfernal and made no attempt to begin a pet battle. So I took the opportunity after a few seconds pause to allow this player the chance - after all they did see it first. In all the excitement I forgot that I'd been leveling other pets and dived straight in with a less than ideal team.
Sadly, my minfernal is only poor quality but I've finally got one!!! For anyone who's interested I'm on Dragonblight (EU) and I captured him at around 20:15 server time. Below is a screenshot so you can see his stats etc.