"One's strongest attack" refers to the most powerful or effective move or action that someone can use in a particular situation. It is a way to describe the most impactful or successful strategy someone has at their disposal. Full definition
That is an interesting choice of example given the current government's strong attack on judicial review proceedings, albeit stopping short of banning them altogether. (newlawjournal.co.uk)
As the fight goes on the boss will attack our hero with stronger attacks. (heypoorplayer.com)
It's essentially a weak and strong attack in which you can string together in various ways to create more complex combos. (ShonenGameZ.com)