Do we have a thread for this already? I couldn't find one. Here's my example for today: Cook Islands $2, 2015 Please post any oddly-shaped coins!
Somehow, I don't have triangular. Oval, Ivan V, 1682-1696: 8-sided Notgeld (always good for an unusual shape): 5-sided(?) Ashoka the Great (273-232BC):
Cook Islands... 3 sided...proof set scarce... Belize 5 sided gold coin... Fiji 5 sided... Belgium Congo 6 sided...
Dodecahedral brass 3d which has split into two halves due to the presence of a large trapped air bubble in the flan.
I think that's dodecagonal. If I remember my wasted youth playing D&D, dodecahedral would be this guy: Speaking of pentagons, here's an approximately pentagonal coin: Attribution says Constans II with horse's head Arab countermark, but I can't really make out anything.
I got these as a gift, along with the rest of the proofs for that year. Images from online, but that's probably better because I can't take very good pictures.....
I usually take my photos with the coin on top of a coin box. I needed three for this one. Sweden 1 daler 1746:
Did you know that one of the sakura flowers along the border will always be inverted? It's location would then show where and when it was minted (I think).
A few more: Japan 1 Shu Japan "bean money" It's shaped a lot like a go stone. Byzantine Billon Trachy, Theodore of Thessalonica, 1224-1230, (cup-shaped) Magadha India ~346 BC Sweden 4 Daler copper plate money, 1756 (still after 1.93 kg after all that corrosion!)