Can someone explain this weird mining activity? I can't figure why this block has 0 coinbase with 0 transactions... however still a valid block? Or it it empty? According to whalepanda this coinbase was sacrificed by unknown miner.

See the block at height
    501,726
It has no transactions other than the coinbase transaction. However, the transaction's coinbase output is 0 BTC. Here's the valuable piece of information that you are looking for:


  Coinbase outputs may be set lower than the max. value (12.5 currently), and the block will be valid (if the difficulty is lower than the target, as always)


Also look at: https://btc.com/0000000000004c78956f8643262f3622acf22486b120421f893c0553702ba7b5

BTW, the miner loses money, for the price of being "cool".