Rocky V
It's revealed in Rocky V that Mickey left his gym to Rocky's son, Robert. By doing this, it kept the IRS from seizing control of the gym after Rocky goes bankrupt due to his accountant's bad deals and tax evasion history. After going into bankruptcy from inability to fight with brain damage, Rocky went back to the old gym and had a flashback to a training session with Micky (which Burgess Meredith reprises the role for) before his fight with Apollo Creed (though it's unknown if this is the fight in Rocky or Rocky II). Micky then gave some important life lessons to Rocky and gave him a necklace that belonged to Rocky Marciano and was passed on to Micky. Rocky began to feel responsible for Micky's death again.
Later during Rocky's street fight with Tommy Gunn, Rocky began having flashbacks of his fight with Ivan Drago, but then Micky appeared and told him, "Get up you son of a bitch! 'Cause Micky loves you." This gave Rocky the strength he needed to defeat his former protégé in said street fight.
This was the last time Burgess Meredith appeared without the use of archival footage, as he died in 1997.
Read more about this topic: Mickey Goldmill, Fictional Biography