How to solve a very HARD CLASSIC SUDOKU ? 

Super excited to solve it . This is the first time I proceeded methodically, filling snyder notations and then looking for the intended solve path( this is the term I heard on this channel) , focussing on the 8 & 9's in boxes 6 and 8 and deciding their positions in col9 and row 9. We hv only two 8's in col 9 and similarly in row 9. If we hv an 8 at R3C9, we get a contradiction. First digit placed is 8 at R9C9. Then I filled some bivalued cells in row9. Similar reasoning for 9's in col 9 , possible just at two places at R3 and R7. In each of these cases 9 is prevented from its occurrence in rt col of box 4. Thus we get snyder 9's in bott row of box 4 at R6(C1+C2) and then in top row of box 5 we hv only two places for 9 in col 9 at R3 and R7, each of these cases prevent R3C4 of col 4 to hv the digit 9 there. Hence #9 can only be at R4C4 in col 4 R4C4=9 Then I got x wing on 8's in rows 1 and 4 at C3/C5 Filled bivalued cells R2C5=47 R2C3=49 The only place for 8 in row 2 is R2C8 R2C8=8 Filled bi valued cells...bla bla bla And yes , in the midd vertical chute applied x wing on 1's to place 1 in box 5. Wow ! Now it's time to watch ur solve.

Using sword fish helped me to some extent. Very good puzzle. Thanks

Thank you for the informative video. Pointing out another way to look into it. I was able to figure out Phistomefel ring will help out in this case. Presence of two 8's in ring ensure that I need to place two 8's in outer squares. After placing 8 since we cannot place 9 in outer squares, we cannot have them in the ring.

प्रारम्भ में 8 & 9 को हम empty cell तकनीक का प्रयोग करके हटा सकते है।

KKS ji, cld u pl explain abt Phisto....ring discussed wrt this video or provide any other link dealing with this strategy.