Re: Hibernate mode on? (videos)
This is a baby European hedgehog. They are allowed to leave the nest without the mother when they are around 5-7 weeks old and weaned (before that she takes them out with her), but they come back until the mother kicks them out at 2 months, they are around 250 grams then. Yours looks really tiny to me, he probably lost his mother. But size can differ. If he wasn't weaned yet, he lacks the milk he needs.
You live in NZ - it's winter there right? If so, he could be hibernating. In NZ they hibernate not that long, only a month or so. They start around July with storing fat in their bodies (under their skin) to make it through winter. Your hedgehog is young and he probably doesn't have enough stored yet. Here they say: if they don't weigh 800 grams, they are not likely to make it through winter. When they don't have enough fat stored they wake from their hibernation, wander around to find food/a new sleeping place and die. It is a big shock to their bodies to wake up and go suddenly from such a low body temperature to a normal one again.
Also, they have something which is a sort of "hibernation gland", IBAT in English (it isn't exactly a gland but you get the idea). Here they store "brown fat" which keeps them warm. They mainly use it at the end of their hibernation, when they wake up. It kick-starts their metabolism again. This fat is located at the shoulder and you should be able to see it. If it isn't enough the hedgehog will die because he can't keep himself warm when waking up in spring. There isn't that much information about it, but I've found this:
Just like any other hibernating mammal, the hedgehog puts on a lot of fat, which not only serves to keep the metabolism going through, at a reduced rate but also helps to provide a stimulus to initiate hibernation. In addition to this there is also a deposit of dark fat and lymph tissue round the blood vessels in the neck, chest and other areas. It is large in autumn but decreases to very small proportions by summer, but at a much slower rate than the general fat reserves. It has been termed as the hibernating gland but its actual functions are as yet obscure. At the beginning of hibernation the general fat deposits are very large, not only under the skin but also in the mesenteries (the thin sheets of tissue that anchor the viscera to their places inside the abdomen). It is these deposits that are used up first so that little fat is removed from the hibernating gland until the end of march. The largest part of the gland lies under the fore arm and is triangular in shape with the apex extending forward closely investing the external jugular vein, a smaller part extends up between the shoulder blades and along the to the base of the skull, and another along the front of the neck to the thymus and thyroid glands.
The gland is lobulated and at the beginning of hibernation is orange brown in colour, structured from lymphoid, glandular and fatty tissues. The amount of water in the hibernating gland varies conversely with the amount of fat. The fat is replaced by water as it is used up even though the animal does not drink. This water logging of tissues is similar to that seen in cases of starvation. The amount of water loss by the body is reduced by a slow down in the kidneys, by a system of short cuts of the smaller blood vessels. This reduces the amount of blood flowing to the surface area which is where the most fluid leaves the blood in the formation of urine.
I've never seen it myself, but maybe this could be your mysterious lump (if there are more)? I can't get a good view of it from the video. Of course only a vet with more experience could know it for sure, it could be something bad. It's good to hear you're taking him there already.
I don't know how things are in NZ but here we have hedgehog sanctuaries, they take care of sick and wounded hedgehogs. This one would've died for certain if you had left him out. I hope he'll make it. It's a good thing you picked him up!