ATTiny85 as a RepeaterNode-just a repeater, no sensors

[Bogus Exception]

Experts,
I have range issues, so I want to use a few ATTiny85s I have to be repeaters.

from the distro:

#define MY_RADIO_NRF24
#define MY_REPEATER_FEATURE
#include <MySensors.h>

void setup(){}

void presentation()
{
	sendSketchInfo("Repeater Node", "1.0");
}

void loop(){}

This appears to be what is needed. Serial is not applicable on stock 85. But burning with 'Arduino as ISP', a TON of compile errors pull up, pointing to internal/lib code. They start like:

Compiling sketch...
"C:\Users\\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\4.9.2-atmel3.5.4-arduino2/bin/avr-g++" -c -g -Os -Wall -Wextra -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -MMD -flto -mmcu=attiny85 -DF_CPU=8000000L -DARDUINO=10802 -DARDUINO_attiny -DARDUINO_ARCH_AVR   "-IC:\Users\\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.6.19\cores\arduino" "-IC:\Users\\AppData\Local\Arduino15\packages\attiny\hardware\avr\1.0.2\variants\tiny8" "-IC:\Users\\Documents\Arduino\libraries\MySensors" "-IC:\Users\\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.6.19\libraries\SPI\src" "C:\Users\\AppData\Local\Temp\arduino_build_538309\sketch\RepeaterNode.ino.cpp" -o "C:\Users\\AppData\Local\Temp\arduino_build_538309\sketch\RepeaterNode.ino.cpp.o"
In file included from C:\Users\\Documents\Arduino\libraries\MySensors/MySensors.h:65:0,

                 from C:\Users\\AppData\Local\Temp\arduino_modified_sketch_726034\RepeaterNode.ino:41:

C:\Users\\Documents\Arduino\libraries\MySensors/core/MyHwAVR.cpp: In function 'void hwPowerDown(period_t)':

C:\Users\\Documents\Arduino\libraries\MySensors/core/MyHwAVR.cpp:66:20: error: 'WDTCSR' was not declared in this scope

  uint8_t WDTsave = WDTCSR;
                    ^

In file included from C:\Users\\Documents\Arduino\libraries\MySensors/core/MyHwAVR.cpp:22:0,

                 from C:\Users\\Documents\Arduino\libraries\MySensors/MySensors.h:65,

                 from C:\Users\\AppData\Local\Temp\arduino_modified_sketch_726034\RepeaterNode.ino:41:

C:\Users\\Documents\Arduino\libraries\MySensors/core/MyHwAVR.cpp: In function 'void hwInternalSleep(long unsigned int)':

C:\Users\\Documents\Arduino\libraries\MySensors/core/MyHwAVR.h:38:25: error: 'Serial' was not declared in this scope

 #define MY_SERIALDEVICE Serial
                         ^
[dotdotdot]
Using library MySensors at version 2.1.1 in folder: C:\Users\\Documents\Arduino\libraries\MySensors 
Using library SPI at version 1.0 in folder: C:\Users\\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.6.19\libraries\SPI 
exit status 1
Error compiling for board ATtiny25/45/85.

This looks a lot like something basic, and not like anything is broken (to me).

If you want the entire ugly STDOUT/ERR, I uploaded to pastebin here.

If folks are using ATTiny85 for sensors, then surely I should be able to make it a simple repeater, no? (please say yes!)

TIA
:)