A little hollow bronze boar was found at (or at least, near) the hillfort, and has been interpreted as an ornament for an Iron Age helmet. It's also known as the Guilsfield boar. It gets a mention in 'An inventory of the ancient monuments of Montgomeryshire' here:
The following extract from a letter of the 1st February, 1833, from Mr. P.G.Mytton, Garth Cottage, Llanfyllin, to the Rev. Walter Davies, is of importance:--
"If you can give me any information respecting a piece of antiquity found on Varchoel Demesne, the property of my uncle, you will very much help him and myself. It is of solid gold in the shape of a wild boar; its weight two ounces, length about two inches, and height about one; it is grooved under the belly longitudinally, the groove about 1/8th inch wide ... I have stated the size from conjecture, not having measured it; but the weight is correct."
The hillfort itself was part of the Garth estate until the mid-twentieth century (as you can read about on the other link). Garth Hall was a rather striking building but now demolished. Calling the boar 'solid gold' was a bit ambitious if it's bronze and hollow, so you can only hope he was more accurate about the animal's origins. By 1871 Archaeologia Cambrensis seemed certain it was found 'within [the] ancient work' of the fort, but 'under what circumstances it was first discovered, and whether associated with any other remains, has not been handed down.' Ah but luckily that sort of thing doesn't happen these days does it? Oh.