Mirko "Cro cop" Filipović (43 years old; 35 W, 11L) came out of retirement once again and fought japanese mma veteran Tsuyoshi Kosaka (47 years old; 29 W, 17 L) at Rizin FF 9 on New Year's Eve and earned a corner/referee stoppage 1 minute into the fight. He won via viscious ground and pound after knocking down Kosaka with powerful punches from the clinch.
https://www.mmafighting.com/2017/12/31/16832960/rizin-ff-9-world-grand-prix-finale-results
Since losing some speed in the last few years he has focused more on the clinch game and it showed in this fight even though Kosaka is not a powerhouse.
I singled out this moment in the fight (gif below) where he's holding Kosaka with his left hand (his power hand) and delivering devastating power with his right hand from short range.
Another example of his power in the clinch was last year when he made enough space to deliver a knee to the liver of Baruto a 180 kg (379 lb) fighter and dropped him. He's grappling power has always been top notch but I think he has gotten even stronger in the last few years.
The Kosaka fight is suppose to be one of the warm up fights leading up to his final retirement fight which is suppose to take place at the end of 2018.
Mirko has gone into retirement a couple of times now (last year's Rizin tournament being the last one) so this is kind of doubtful.
Personally from what I've seen in this fight he's wasting time in Japan. He has no real competition there. If he's being cautious to preserve health I understand.
As a fan I'd like to see him fight the best or at least avenge some losses in the UFC while he is in top shape.
Maybe it's a bit selfish for me to want him to risk his health at this age against the best fighters but as he's my favorite fighter I always want to see him fight the best.