Syndicate use the "Indentured" keyword for many abilities. For example the Overseer can add an extra turn to an indentured units and and add +10% crit just by being around. Other non-Syndicate biological units of T1-T2 can be outfitted by control collars so that they can also receive Indentured buffs and abilities which can make interesting combos as well potentially reduce their energy upkeep by 50%. Their support units have AOE shielding that also applies Psionic buff effects. Syndicate can be played as a powerful swarm faction rivaling even Ki'rko.
Syndicate has access to Psi and Arc weapons Psi is strong against Biological/Cyborg and Arc against Mechanical targets so balance them accordingly. The Psi weapon tree is especially versatile offering both defensive and offensive capabilities and some of the strongest Debuffs/CC in the game. Notably the Arc Retaliation Defense is one of the most annoying defensive mod.
Syndicate buffs Flanking attacks which are +20% dmg by default, use the Hallucinating debuff makes the target always flanked and have -30% accuracy.
Syndicate Enforcers are one of the few units in the game that have a melee attack with Psi damage. This is notable because this ignores both Armor and Shields making them deal devastating damage in melee against enemies with no Psi resist. Note that all mechanical units have an innate +4 psi resist which cannot be ignored with Psi damage in any way but can be lowered by Broken Mind.
On the economy side of things Syndicate have some of the best Operations bonuses both on offense and defense rivaled only by Shakarn. Thus they can indirectly weaken their enemies by stealing Research or Energy and using any offensive operations their Secret tech has to offer. They also benefit from improved Influence Generation which is a rare resource for other factions. In the lategame they can also enhance the frequency and results of happiness events.