Following the 2018 election and a long phase of negotiations, Lega and the Five Star Movement (FSM) appointed the first cabinet in Western Europe that does not include any mainstream party family. The ‘elective affinities’ between the electorates of these two challenger parties had been quite evident for some time, but in the present work we argue that there are further traits that the two parties had shared well before 2018 that could help to further prove their proximity. We propose a new dimension of analysis that should be taken into consideration when studying (new) challenger parties: their relationship vis-à-vis the other opposition parties. We would expect them to enter parliament for the first time with both the goals usually related to the two different opposition status (temporary vs. permanent) in mind: leaving the opposition and exploiting the opposition. Furthermore, we would expect them to stand apart from the other parties, no matter whether the latter are in government or in opposition. This is, in fact, one of the main reasons for their electoral success and, in the end, their essence. We will test these expectations by employing Social Network Analysis methods and analysing and comparing the cooperation attitudes of the Lega and FSM with the other opposition parties, using as an indicator the amount of legislative co-sponsorship during their first term in parliament (respectively 1992-1994 and 2013-2018) and the amount passed together while in opposition (2013-2018).