ATMEL ATTINY85 - How to switch clock to 128 kHz or less?

Using Arduino Microcontrollers
8

mpcz:
Support for IDE ATTINY85 / 128 kHz was successful.
Unfortunately, the delay () command does not work. Here the program is blocked.
Is command "delay()" in 128kHz mode operational?
Thanks, mpcz, 02.oct.2017

p.s. (target = minimum consumption, no current peaks over 300 microA).

What core are you using?