Hope people don't mind me interrupting the "tag" solution for A64V2 to post my walkthrough for the original Assassin.
Only finished it yesterday and then worked through Para's and Cathy's walkthroughs today before deciding to post it. I agree with Para that it's rated between 1.0 and 1.25
I seem to have done more with the combinations for sub-cages, which is unusual for me, but they were helpful this time. I would have finished earlier but I found I'd deleted one combination too many from a sub-cage, which happened to be part of the solution.
Still that's better than deleting a different combination and having a flawed solution path.
Lots of killers, which I enjoyed.
Here is my walkthrough for A64.
1. R12C1 = {49/58/67}, no ,1,2,3
2. R12C9 = {15/24}
3. R23C6 = {16/25/34}, no 7,8,9
4. R78C4 = {18/27/36/45}, no 9
5. R89C1 = {17/26/35}, no 4,8,9
6. R89C9 = {19/28/37/46}, no 5
7. 8(3) cage in N1 = 1{25/34}, 1 locked for N1
8. R456C1 = {128/137/146/236/245}, no 9
9. R456C9 = {289/379/469/478/568}, no 1
10. R5C678 = {128/137/146/236/245}, no 9
11. 20(3) cage in N7 = {389/479/569/578}, no 1,2
12. 23(3) cage in N9 = {689}, locked for N9, clean-up: no 1,2,4 in R89C9
12a. Naked pair {37} in R89C9, locked for C9 and N9
13. 27(4) cage in N2 = {3789/4689/5679} = 9{378/468/567}, no 1,2, 9 locked for N2
14. 30(4) cage at R3C1 = {6789}
15. 14(4) cage at R6C2 = {1238/1247/1256/1346/2345}, no 9
16. 13(4) cage at R6C7 = {1237/1246/1345} = 1{237/246/345}, no 8,9
17. 45 rule on R5 3 innies R5C159 = 19 = {289/379/469/478/568}, no 1
18. 45 rule on N5 2 outies R37C5 = 2 innies R5C46, specifically that R37C5 and R5C46 must contain the same two numbers, in other words Law of Leftovers.
19. 45 rule on C1 2 innies R37C1 = 13 = {67}/[85/94], R7C1 = {4567}
20. 9 in C1 locked in R123C1, locked for N1
20a. 9 in C1 locked in R123C1 -> 4 in C1 must be in R12C1 or R7C1 (R12C3 and R37C1 are both 13(2) cages), locked for C1
20b. R456C1 (step 8) = {128/137/236}, no 5
21. 45 rule on C9 2 innies R37C9 = 10 = [64/82/91]
22. R9C678 = {149/158/248/257} -> R9C6 = {789}
22a. R9C78 = {14/15/24/25} -> R7C89 = {14/15/24/25} (cannot be {12/45} which clash with R9C78)
22b. 13(4) cage at R6C7 = {1246/1345} (cannot be {1237} because R7C89 cannot be {12} from step 22a), no 7
22c. {1246} = {16/26} in R6C78, {14/24} in R7C89
22d. {1345} = {34/35} in R6C78, {14}/[51] in R7C89
22e. R6C78 = {16/26/34/35}, R7C89 = {14/24}/[51] -> R9C78 = {15/24/25}
22f. R456C9 (step 9) = {289/469/568}
22g. R6C78 = {16/34/35} (cannot be {26} which clashes with R456C9), no 2
23. 45 rule on C789 3 outies R159C6 = 13 = {139/148/157/238/247} (cannot be {256/346} because only 7,8,9 in R9C6) -> R15C6 = {13/14/15/23/24}, no 6,7,8
23a. If R15C6 = {23/24} -> R23C6 = {16}
23b. Killer single 1 in R15C6 and R23C6, locked for C6
[Alternatively 45 rule on C6 4 innies R4678C6 = 25 but cannot be {1789} which clashes with R9C6 -> no 1]
24. 45 rule on C123 3 outies R159C4 = 11 = {128/137/146/236/245}, no 9
25. 45 rule on R89 4 outies R7C3467 = 30 = {6789}, locked for R7, clean-up: no 6,7 in R3C1 (step 19), R8C4 = {123}
26. Killer pair 4,5 in R7C1 and R7C89 (step 22e), locked for R7
27. 45 rule on N1 2 innies R3C12 – 10 = 1 outie R1C4, min R3C12 = 14, max R3C12 = 17 -> R1C4 = {4567}
28. 45 rule on N7 2 innies R7C12 – 4 = 1 outie R9C4
28a. R7C12 = [42/43/51/52/53] (cannot be [41] which clash with R7C89) -> R9C4 = {234}
29. 45 rule on N8 3 innies R7C5 + R9C46 = 13 = {139/148/247} (cannot be {238} which clashes with R78C4)
29a. 1 of {139} in R7C5 -> no 3 in R7C5
29b. 2 of {247} in R7C5 -> no 2 in R9C4
30. R7C2 = 3 (hidden single in R7), clean-up: no 5 in R89C1
30a. 14(4) cage at R6C2 = {1346/2345} (cannot be {1238 because R7C1 only contains 4,5} = 34{16/25}, no 7,8
31. 3 in C1 locked in R456C1 (step 20b) = {137/236}, no 8, 3 locked for N4
31a. Killer pair 1,2 in R6C23 (step 30a) and R456C1, locked for N4
31b. Min R5C23 = 9 -> max R5C4 = 6, clean-up: no 7,8 in R3C5 (step 18)
32. Hidden killer pair 1,2 in R89C1 and R9C23 -> R9C23 must contain 1/2
32a. R9C234 = {139/148/238/247} (cannot be {157/256} because R9C4 only contains 3,4), no 5,6
32b. 20(3) cage in N7 = {479/569/578}
32c. Killer pair 4,5 in R7C1 and 20(3) cage, locked for N7
32d. Killer pair 6,7 in R89C1 and 20(3) cage, locked for N7
32e. R9C234 = {139/148/238}
32. 8 in C1 locked in R123C1, locked for N1
32a. Killer pair 6,7 in R456C1 (step 31) and R89C1, locked for C1
32b. Killer pair 4,5 in R12C1 and 8(3) cage, locked for N1
33. R1C234 = {257/347/356}
33a. 4,5 only in R1C4 -> R1C4 = {45}
33b. 3 of {356} in R1C3 -> no 6 in R1C3
34. R3C12 – 10 = R1C4 (step 27)
34a. R1C4 = {45} -> R3C12 = 14,15 = [86/87/96], R4C23 = {69/78/79}
34b. 45 rule on R123 5 innies R3C12589 = 28, min R3C1259 = 21 -> max R3C8 = 7
35. 45 rule on N2 3 innies R1C46 + R3C5 = 11, max R1C46 = 9 -> min R3C5 = 2
35a. R1C46 + R3C5 = {146/245} (cannot be {236} because only 4,5 in R1C4) = 4{16/25}, no 3, 4 locked for N2, clean-up: no 3 in R23C6, no 3 in R5C46 (step 18)
35b. Killer pair 5,6 in R1C46 + R3C5 and R23C6, locked for N2
35c. 1 in N2 locked in R123C6, locked for C6
36. R5C678 = {128/146/236/245} (cannot be {137} because R5C6 only contains 2,4,5), no 7
37. 7 in N6 locked in R4C78, locked for R4 and 20(4) cage at R3C8
[This makes R3C2 a hidden single in the 30(4) cage but step 37a does more!]
37a. R4C23 (step 34a) = {69} (only remaining combination), locked for R4, N4 and 30(4) cage at R3C1 -> R3C12 = [87], R7C1 = 5 (step 19), clean-up: no 2 in R456C1 (step 31), no 2 in R7C9 (step 21)
38. Naked triple {137} in R456C1, locked for C1 and N4
39. Naked pair {24} in R6C23, locked for R6 and N4
39a. Naked pair {58} in R5C23, locked for R5 -> R5C4 = 2, R5C6 = 4 -> R37C5 = [42] (step 18), R9C46 = [47] (step 29), R1C4 = 5, R89C9 = [73], clean-up: no 2 in R23C6, no 1 in R2C9
40. R7C3 = 7 (hidden single in C3), R1C6 = 2 (hidden single in N2), R1C23 = [63], clean-up: no 4 in R2C9
41. Naked pair {26} in R89C1, locked for N7
41a. 20(3) cage in N7 = {479} (only remaining combination) -> R8C23 = {49}, locked for R8 and N7
41. Naked pair {14} in R7C89, locked for 13(4) cage at R6C7
41a. 13(4) cage at R6C7 = {1345} (last remaining combination) -> R6C78 = {35}, locked for R6 and N6
42. 9 in N6 locked in R456C9, locked for C9 -> R3C9 = 6, R5C9 = 9, R6C9 = 8, R4C9 = 2, R7C9 = 4 (step 21), R7C8 = 1, R12C9 = [15], R23C6 = [61]
43. Naked pair {68} in R8C78, locked for R8 and N9 -> R7C7 = 9, R89C1 = [26]
44. R5C78 = [16]
45. R1C6 = 2 -> R1C78 = 16 = [79]
46. R3C9 = 6, R4C78 = {47} -> R3C8 = 3 (cage sum)
and the rest is naked singles