As for me, the ideal armor for an assassin is an armor in which he is not just not visible and not heard, but also an armor in which it is very easy to move. She should not have protection because the assassin's job is that he kills the target unnoticeably and she simply will not be able to attack in response. Possible functions of such armor. Simple options. dash (teleport) or stealth. The options are more complicated. Moving into the shadow of a character (roughly speaking, linking one person to another with the disappearance or serious reduction of the hitbox) or, for example, for a particularly cruel killer, absorbing the souls of killed mobs to activate invisibility, dash (teleport) (this is just a variant of complicating simple mechanics). it is possible to increase the height of the jump or a hook for clinging to the elements of the landscape.
Summing up, this is a light, comfortable and secretive armor, possibly with the above listed functions, which has very little protection.
(I'm sorry if the translator translated badly)
Addition 1
Well, after reading the comments of other people, I would like to supplement my words. In addition to the assassin to which we are all accustomed, there are other options for combat. An assassin is a rudely burning person whose main occupation will be killings. Therefore, the assassin can choose different paths to achieve his goal. Perhaps he will poison his target with poison, or (which applies to armor) install a combustible gas sprayer on his suit and then set it on fire. And boom, nobody's alive. But in this case, the assassin must also be able to defend himself from himself. That is, the assassin's armor depends solely on how this assassin is played. BUT each armor should have both its advantages and disadvantages. (maybe it sounded corny, but I often met cases and I myself was like that, people wanted to create perfect armor without minuses, but this does not happen :( )