If Caitlyn deals 3 damage to an 11 might Dr. Mundo and it gets stunned, then Leona (who reduces enemy might by 8) moves to that battlefield, does Dr. Mundo die immediately? If so, when does this happen and can players respond?

Ruling: Yes, Dr. Mundo will die. Leona's passive applies immediately when she is located at the battlefield, and Dr. Mundo dies during the cleanup after her movement, before combat is staged or opened.

Sequence:

• Leona moves to the battlefield
• Leona's passive applies immediately (Dr. Mundo now has 3 might and 3 damage)
• During cleanup step 2b, Dr. Mundo dies as a state-based action
• Combat is staged in step 7 and opened in step 10

Nuances:

• The passive applies without using the chain or cleanup
• Players cannot respond before Dr. Mundo dies - it happens before anyone has a chance to play cards or respond
• This all occurs before combat has even opened