Board Thread:Theories and Speculation/@comment-45444155-20200806213256/@comment-31715856-20200806225934

If you're talking about the Curse Mark, the answer is that it is considered to be a kind Senjutsu, even listed as such on this Wiki. Juugo granting Sasuke's Susanoo with the rough equivalent of Sasuke's Curse Mark was dubbed by Orochimaru a "Senjutsu Susanoo", so we get this from in the series. Using Senjutsu chakra, even if not in Sage Mode per se, is Senjutsu. Sage Mode requires balancing that external energy, so anything lesser than that isn't SM, even if through unknown means the user uses the energy to up their power to a lesser degree than true SM.

I mean think about it, Jiraiya couldn't ever enter the true Sage Mode, but all his jutsu in that form are still considered Senjutsu.