I'm planning to control wirelessly the lights of my house using attiny85 and relays. Since I'm already connecting some part of the circuit (i.e., the relay) to the main power line, i'd like to know if is there any way to power the mc without using an external wall wart adapter. The key point in this project is that I need things to be small, so I can fit them inside the wall switch.
In theory, yes there are and there is such circuitry methods published on the web. But I would fall back on the 'if you have to ask you probably shouldn't be messing with it' line. There is always risks of fire and human safety when DIY methods are applied to household power circuits and I try not to encourage such projects but rather suggest you always use fully UL approved components and assemblies for such applications.