As TVF pointed out, Breach lowers ship speed.
The main strategy to using Executor effectively is to spread breach as much as possible against your opponents. This allows your unbreached ships to effectively take more turns than the enemy’s. It is *the* deciding strategy in mirror-matches, as inflicting breach reduces the ultimate ability cooldown… and in executor mirror-match, first to their ultimate wins.
While RNG is also a heavy factor in all executor battles, typically your best strategy in mirror matches is to inflict breach on the opponent’s Razor Crest ASAP, while cleansing your own Razor Crest of breach when you can.
Because Razor Crest targets an ally to assist (inflicting Breach if you’re smart), having your razor crest take more turns than your opponent’s is extremely helpful in getting your ultimate first.
Hope this helps
