He's the only player to score more than 15 goals in one season at the UCL . He did not only do it once or twice but three solid times.

He has a total of 40 goals at the UCL (both quarter final, semi-final, and final). That’s about 2.5x time as many as any other player in the history of the competition scored in said stages.

Ronaldo’s 40 is also one more than the 2nd, 3rd, 4th, and 5th highest goalscorers in the competition’s history combined scored in said stages.

He has been the top goal scorer in UCL since 2012. Secondly, most of his goals have come deep into the competition playing against the top European teams

He scored at least 10 goals at the UCL for 7 consecutive seasons. No player has achieved this feat for more than 2 consecutive seasons. Ronaldo actually does did

No other player in the history of UCL has ever dominated the tournament to near to Ronaldo.

If there are other things I didn't mention, you can add it in the comment section