Nothing special, just two flashing LEDs 🙂

The 555 TARDIS hooked up as a LED-flasher

This is the schematic I used: TARDIS-atable (note that it is for 555 TARDIS v1.0)
The components making the LEDs flash are as follows: R1=15K, R2=1K, and C1=100µF, the power source is 6-9V.