X-Strike is a Tech in Chrono Trigger usable by Crono and Frog. X-Strike becomes available once Crono and Frog learn Cyclone and Slurp Slash, respectively. Although Frog is not officially recruited until after the Masamune is reforged by Melchior and the Hero's Badge is recovered from Tata, this tech can be learned as early as Crono's first visit to the Middle Ages. In Chrono Cross, a Tech performed by Serge and Glenn exists with the name of X-Strike. quite similar in appearance to its Chrono Trigger counterpart, it is worth noting that Serge, like Crono, is a silent protagonist and Glenn is very similar to Frog. The two not only share the same name but the same spelling of that name, which is an atypical spelling for that name.
Boss Battle Strategy
Fighting Yakra in Manolia Cathedral, Crono, Frog, and Lucca have few options for performing effective hits on the Fiend. Lucca's Flamethrower is all but useless, due to Yakra's high Magic Defense. Because of this, it is advisable to use X-Strike, while Lucca heals the party using Potions and Ethers.
In addition to the Boss battle against Yakra, when battling Flea in Fiendlord's Keep, it is also quite useful to perform X-Strike. Not only are Crono and Frog necessary party members for that boss battle, but the tech proves useful, as Flea also has a high resistance to Magic.