Which engine did they use?

[*Yuki*]

was it unity or gamemaker or anything else?

[*Yuki*]

answered myself: according to wikipedia, this game was made with construct https://en.wikipedia.org/wiki/Iconoclasts_(video_game)

[Kein Zantezuken]

https://twitter.com/konjak/status/833643260740505600

[Quest]

"they"

It's just one guy.

[Icecreammouth]

I hope x360ce works on that engine.