Oh I see, so this is kind of like with Ruby, where people build a lot of magic that looks simple but hides complexity that you still need to understand.
No. Unlike Ruby, Kotlin is compiled and you can't monkeypatch things, so unless you go out of your way to do reflection magic (something that is unfortunately common in the Java community), you won't get weird runtime surprises like not knowing where a method comes from.
I'd say the magic of Kotlin comes down to a few syntactic constructs that compose very well. Also, a decent type system helps with understanding any magic, even those not tastefully created.