According to Russian sources Putin and the North Korean dictator strengthened their military ties with a formal mutual defense pact, which, should the North launch an attack on South Korea, whould bring Russia formally to the defense of North Korea when the South responded to the north’s attack.
The Russians and the NORKs just agreed to use any means available to each other’s mutual defense. That means nukes and Russia is the world leader in tactical nukes they never got rid of them like the USA did. They have slews of battlefield munitions from 10kt artillery shells to hypersonic zircons with 100+kt boosted. It’s always been Soviet and Russian policy to use tactical nukes if they are losing ground. They don’t use strategic level PAL links their individual battlefield commanders have special weapons release codes and the keys to use them. This was first learned in the Cuban crisis and remains the same today.