Thanks manu for a really challenging Assassin. I found it much harder than udosuk and Afmob and, having now read their posts, I see that I missed their nice interactions between Innies for R789 and the 7(2) cage in N9 and I also missed Outies for N1245. Without those steps I think it's a much harder puzzle. However it did allow me to make some interesting "clone" steps.
Here is my walkthrough.
Prelims
a) 8(2) cage in N1 = {17/26/35}, no 4,8,9
b) R1C34 = {39/48/57}, no 1,2,6
c) R12C5 = {17/26/35}, no 4,8,9
d) R1C67 = {14/23}
e) 13(2) cage in N3 = {49/58/67}, no 1,2,3
f) 9(2) cage in N1 = {18/27/36/45}, no 9
g) R23C4 = {17/26/35}, no 4,8,9
h) R23C6 = {59/68}
i) 12(2) cage in N3 = {39/48/57}, no 1,2,6
j) R67C1 = {17/26/35}, no 4,8,9
k) R67C9 = {49/58/67}, no 1,2,3
l) 11(2) cage in N7 = {29/38/47/56}, no 1
m) 7(2) cage in N9 = {16/25/34}, no 7,8,9
n) 13(2) cage in N7 = {49/58/67}, no 1,2,3
o) 11(2) cage in N9 = {29/38/47/56}, no 1
p) R9C34 = {17/26/35}, no 4,8,9
q) R9C67 = {14/23}
r) 9(3) cage in N6 = {126/135/234}, no 7,8,9
s) 35(6) cage in N8 = {146789/236789/245789/345689}, 8,9 locked for N8
1. 45 rule on C123 2 outies R19C4 = 5 = [32/41], clean-up: R1C3 = {89}, R9C3 = {67}
1a. Killer pair 3,4 in R1C4 and R1C67, locked for R1, clean-up: no 5 in R2C3, no 5 in R2C5, no 9 in R2C7
1b. Killer pair 1,2 in R9C4 and R9C67, locked for R9, clean-up: no 9 in R8C7
1c. 13(2) cage in N7 = {49/58} (cannot be {67} which clashes with R9C3), no 6,7
2. 45 rule on N1 2 innies R1C3 + R3C1 = 12 = [84/93]
2a. Max R3C1 = 4 -> min R4C12 = 11, no 1
3. 45 rule on N7 2 innies R7C1 + R9C3 = 8 = [17/26], clean-up: R6C1 = {67}
4. 45 rule on N3 2 innies R1C7 + R3C9 = 5 = {14/23}
4a. Max R3C9 = 4 -> min R4C89 = 11, no 1
5. 45 rule on N9 2 innies R7C9 + R9C7 = 10 = [64/73/82/91], clean-up: no 8,9 in R6C9
[And now the 45 I spotted when I was setting up and colouring the diagram, although I only saw the CPE when I reached this step.]
6. 45 rule on N5 2 outies R37C5 = 15 = [87/96]
6a. 8,9 in N2 locked in R3C5 + R23C6, CPE no 8,9 in R45C6
7. 45 rule on N8 3 innies R7C5 + R9C46 = 10 = {127/136}, no 4, 1 locked for R9 and N8, clean-up: no 9 in R7C9 (step 5), no 4 in R6C9
8. 45 rule on C789 2 outies R19C6 = 5 = [23/32/41], no 1 in R1C6, clean-up: no 4 in R1C7, no 1 in R3C9 (step 4)
9. 45 rule on R123 3 innies R3C159 = 15 = {249/348}, 4 locked for R3, clean-up: no 5 in R2C1, no 8 in R2C9
10. 45 rule on R789 3 innies R7C159 = 15 = {168/267}, 6 locked for R7, clean-up: no 5 in R8C1, no 1 in R8C9
10a. 7 of {267} must be in R7C5 (R7C159 cannot be [267] because R6C19 cannot be [66]), no 7 in R7C9, clean-up: no 6 in R6C9, no 3 in R9C7 (step 5), no 2 in R9C6, no 3 in R1C6 (step 8), no 2 in R1C7, no 3 in R3C9 (step 4)
11. 45 rule on R789 2 outies R6C19 = 1 innie R7C5 + 6
11a. R7C6 = {67} -> R6C19 = 12,13 = {57/67}, 7 locked for R6
12. Hidden pair 1,2 in R1C7 + R3C9 and 15(3) cage for N3, R1C7 + R3C9 contains one of 1,2 -> 15(3) cage must contain one of 1,2 = {159/168/258/267} (cannot be {249} which clashes with R3C9), no 3,4
13. Combined cage R1239C4 = 13 = {1237/1345} (cannot be {1246} which clashes with R1C6 because {1246} must be 4{26}1), no 6, 1,3 locked for C4, 3 also locked for N2, clean-up: no 5 in R1C5, no 2 in R23C4
13a. Killer pair 6,7 in R12C5 and R7C5, locked for C5
14. 45 rule on C12 4 outies R2378C3 = 15 = {1239/1248/1257/1347/1356/2346}
14a. 9 of {1239} must be in R8C3 -> no 9 in R37C3
14b. 5 of {1257/1356} must be in R8C3 -> no 5 in R37C3
15. 45 rule on N6 3 innies R4C89 + R6C9 = 18 = {279/378/459/567} (cannot be {369/468} because R6C9 only contains 5,7)
15a. 18(3) cage at R4C7 = {189/378/459/468} (cannot be {279/369/567} which clash with R4C89 + R6C9), no 2
16. R1C3 + R3C1 = [84/93]
16a. 16(3) cage in N1 = {169/178/259/268/457} (cannot be {349} which clashes with R3C1, cannot be {358} which clashes with R1C3 + R3C1, cannot be {367} which clashes with 8(2) cage), no 3
17. 45 rule on C89 4 outies R2378C7 = 22 = {1579/1678/2569/4567} (other combinations clash with 18(3) cage at R4C7), no 3, clean-up: no 8 in R9C8
18. 7(2) cage in N9 = {16/25/34}, R7C9 + R9C7 (step 5) = [64/82] -> combined cage R7C89 + R8C9 + R9C7 = {1628/2546/3428}, 2 locked for N9, clean-up: no 9 in R9C8
18a. 9 in N9 locked in 17(3) cage = {179/359}, no 4,6,8
[At this stage I remembered that this Assassin had been created by manu. First I spotted “clones” connected with the 30(5) and 30(6) cages in N5, R3C5 must equal one of R6C46 and R7C5 must equal one of R45C46, but I was never able to use these.
Then I spotted that the “clones” around the edges were more helpful at this stage.]
19. 45 rule on N69 1 outie R3C9 = 1 innie R9C7
19a. 2 in C7 locked in R39C7, R3C9 = R9C7 -> 2 locked in R3C79, locked for R3 and N3, clean-up: no 7 in R2C1
19b. 15(3) cage in N3 (step 12) = {159/168/258/267}
19c. 2 of {267} must be in R3C7 -> no 7 in R3C7
20. 45 rule on N7 1 outie R6C1 = 1 innie R9C3
20a. 7 in R6 locked in R6C19 (step 11a), R6C1 = R9C3 -> 7 locked in R6C9 + R9C3, CPE no 7 in R9C9
21. 7 in N5 locked in 30(6) cage at R3C5
21a. 30(5) cage at R5C5 = {15789/24789/25689/34689/45678} (cannot be {35679} because not possible to make 30(6) cage at R3C5 with 1,2,4,7), 8 locked for N5
22. R7C5 = {67} -> R6C19 = 12,13 = {57/67} (step 11a)
22a. R7C5 = 6 => no 6 in R6C46
22b. R7C5 = 7 => R6C19 = 13 = {67}, locked for R6
22c. -> no 6 in R6C46
23. 30(5) cage at R5C5 = {15789/24789/25689/34689} (cannot be {45678} because 6,7 only in R7C5), 9 locked for N5
24. R3C9 = R9C7 (step 19) = {24}
24a. All cells in N6 except for R56C8 “see” at least one of R3C9 or R9C7 -> R56C8 must contain at least one of 2,4 -> 9(3) cage in N6 = {126/234} (cannot be {135} which doesn’t contain 2 or 4), no 5, 2 locked for N6
25. R4C89 + R6C9 (step 15) = {378/459/567}
25a. 18(3) cage at R4C7 (step 15a) = {189/378/459} (cannot be {468} which clashes with R4C89 + R6C9), no 6
26. 6 in C7 locked in R2378C7 (step 17) = {1678/2569/4567}
26a. 2 of {2569} must be in R3C7 -> no 9 in R3C7
27. 45 rule on N1 1 outie R1C4 = 1 innie R3C1 = {34}
27a. All cells in N3 except for R2C789 “see” either R1C4 or R3C1 -> R2C789 must contain one of 3,4 (R2C789 cannot contain both because R1C7 + R3C9 contains one of 3,4)
27b. Killer pair 3,4 in R1C7 + R3C9 and R2C789, locked for N3, clean-up: no 9 in R2C9
[Note that 3,4 have already been eliminated from R2C8 but the logic above reads better when saying R2C789.]
28. 16(3) cage in N1 (step 16a) = {169/178/268/457} (cannot be {259} because R3C3 only contains 1,6,7,8)
28a. 4 of {457} must be in R2C2 -> no 5 in R2C2
29. 45 rule on N7 1 outie R9C4 = 1 innie R7C1 = {12}
29a. All cells in N9 except for R8C789 “see” either R7C1 or R9C4 -> R8C789 must contain at least one of 1,2
[Similar comment to note after step 27, no 1,2 in R8C7.]
30. R8C89 contains at least one of 1,2
30a. R8C8 = 1 => 17(3) cage in N9 = {179}
30b. R8C9 = 2 => R7C8 = 5 => 17(3) cage in N9 (step 18a) = {179} (cannot be {359} when R7C8 = 5)
30c. -> 17(3) cage in N9 = {179} -> R9C9 = 9, R7C7 + R8C8 = {17}, locked for N9, clean-up: no 4 in R8C3, no 6 in R8C9, no 4 in 11(2) cage in N9
31. R7C159 (step 10) = {168/267}
31a. Killer pair 1,7 in R7C159 and R7C7, locked for R7, clean-up: no 4 in R8C1
32. 9 in C7 locked in 18(3) cage at R4C7, locked for N6
32a. 18(3) cage at R4C7 (step 25a) = {189/459}, no 3,7
33. R1C7 = 3 (hidden single in C7), R1C4 = 4, R1C3 = 8, R1C6 = 2, R9C6 = 3 (step 8), R9C7 = 2, R9C4 = 1, R9C3 = 7, R7C1 = 1 (step 29), R6C1 = 7, R6C9 = 5, R7C9 = 8, R7C7 = 7, R8C8 = 1, R7C5 = 6, R3C5 = 9 (step 6), R3C9 = 2 (step 4), R3C1 = 4 (step 2), clean-up (working across in nonets, rather than rows): no 1 in R1C2, no 6 in R2C3, no 1,5 in R3C2, no 7 in R23C4, no 5 in R23C6, no 6 in R1C8, no 5 in R2C7, no 7 in R3C8, no 4 in 18(3) cage at R4C7 (step 32a), no 5 in 7(2) cage in N9
34. Naked triple {189} in 18(3) cage at R4C7, locked for C7 and N6, clean-up: no 6 in 9(3) cage in N6 (step 24a)
35. R4C89 = {67} (hidden pair in N6), locked for R4
36. R2C7 = 4 (hidden single in C7), R1C8 = 9, R2C9 = 7, R3C8 = 5, R12C5 = [71], R3C7 = 6, R1C9 = 1, R2C8 = 8, R23C4 = [53], R23C6 = [68], R3C2 = 7, R2C1 = 2, R2C3 = 3, R1C2 = 5, R1C1 = 6, R2C2 = 9, R3C3 = 1, R4C89 = [76], R8C7 = 5, R9C8 = 6, R8C3 = 9, R9C2 = 4
and the rest is naked singles.