Which Wales v Scotland?
An unanswered 38 points from 31-0 down to end in a draw in the last minute is easily the greatest comeback.
From wiki:
Notes:
This was the highest-scoring draw in international rugby history at 76 total points scored.
This was the first time England had conceded a try bonus point in the Six Nations; they became the final team to do so since bonus points were introduced in 2017.
Scotland retained the Calcutta Cup; this was the first time since 1984 they had done so, and the first time since 1989 they had not lost to England at Twickenham (the 1989 match was also a draw).
The 24-point half-time deficit (and 31-point deficit after 30 minutes) Scotland turned around, was the largest comeback for a draw in international rugby history, beating their own previous record against Wales in 2001.
With Jonny May's try in the 31st minute, England earned the fastest bonus point try in the Six Nations, beating the previous record they set against Italy the previous week.
Scotland's six tries were the most they had scored in a match at Twickenham.