In Sonic Forces, Sonic the Hedgehog series: Shadow the Ultimate Lifeform never explained why he killed the Jackal Squad (except Infinite; the Ultimate Mercenary) in the first place.
Why? Because he doesn't care.
Infinite (former Jackal Squad leader; the Ultimate Mercenary) reaction Shadow the Ultimate Lifeform and Rouge the Bat (from Sonic Forces, Sonic the Hedgehog series)
Infinite (former Jackal Squad leader; the Ultimate Mercenary) reaction Sonic and Amy Rose (from Sonic X, Sonic Forces, Sonic the Hedgehog series)
Besides Shadow the Hedgehog (2005 video game), and Sonic and the Black Knight;
Infinite (former Jackal Squad leader; the Ultimate Mercenary) is/was the only swordfighter in Sonic Forces (from Sonic the Hedgehog series)
For future Sonic the Hedgehog series: I really want Infinite (former Jackal Squad leader; the Ultimate Mercenary):
1.) To become a cyborg or something
2.) Upgrade both his Phantom Ruby Prototype, and his sword into something special
For future Sonic the Hedgehog series: Team Dark (Shadow the Ultimate Lifeform, Rouge the Bat, E-123 Omega) vs. Infinite as a cyborg (former Jackal Squad leader; the Ultimate Mercenary)
Infinite (former Jackal Squad leader; the Ultimate Mercenary): Before and After (from Sonic Forces, Sonic the Hedgehog series)
1.) Jackal Squad leader
2.) Master of Illusions and the Phantom Ruby
3.) (possibly) Becoming a cyborg or something else?
@NibrocRock Mana the Hedgehog/Dark reaction of Ghost Sonic and Ghost Tails (from Sonic Rivals 2, and Sonic Forces, Sonic the Hedgehog series)
1) Infinite (former Jackal Squad leader; the Ultimate Mercenary) will never become a better warrior and a better rival like Tai Kamiya, Agumon (as WarGreymon), Matt Ishida, and Gabumon (as MetalGarurumon) or anyone else (from Digimon, and Sonic Forces, Sonic the Hedgehog series)