enworld上一个老外提出的改法，感觉有点意思
Assassinate (Enhancement)
As a bonus action you can plan a telling blow on a target who isn't hidden from you. Roll 1d20 and keep it as your assassination die on that target for 1 minute. You can use the value of this assassination die to replace an attack roll on the target, and then it is expended. At the start of each of your turns you may increase the value of the assassination die by 1, to a maximium of 20. If you use this bonus action again you can choose to keep the old assassination die and target, or use the new roll and target. If you are hidden from the target or the target is unaware you are hostile to them, roll twice and keep the better result. At 9th level you instead increase your assassination die by up to 1d4 at the start of your turn, at 13th by up to 1d6, and at 17th up to 1d8.
