You can complete nearly all Jack's achievements @ Act IV Ch 1.
At this point you should have alot of component points left to get
Barrier (Take all 3 abilitys)
STIM (Just Revive; cost 8)
Cloak (Speed + Duration)
Hijack (Duration)
Shock trap (Nothing needed)
Flash (Range)
Load it up, get to the point where the swarmak is, and rush to the warden
-> Use Barrier and reflect bullets of some drones - you should leave at least one
The Back Atcha achievement in Gears 5 worth 34 pointsGet a kill with ricochet bullets using Jack's Barrier Ability -> let ur Teammate get downed by the warden and use STIM for revive
-> Hijack him and let the warden get a kill, thats why u should leave a drone
(1/4)
The An Enemy Among Us achievement in Gears 5 worth 62 pointsGet a kill with a Hijacked Pouncer, Warden, Stump and Elite Hunter in Campaign Proceed further to the Rejects
->Use Cloak , and get the 3 kills for
The Seraninja achievement in Gears 5 worth 25 pointsUse Jack's Cloak ability to cloak and execute 3 enemies before de-cloaking in Campaign ->Reload checkpoint . rush in, take right path until you come to this room and use Shock Trap to hit 6 enemies
The Shock and Awe achievement in Gears 5 worth 18 pointsUse Jack's Shock Trap ability to shock 6 enemies at once in Campaign ->Reload, repeat and use Flash instead - hit atleast 3, you can do it earlier too.
->Reload if you want to get 100 Reject Execute - takes about ~15 min
In the next Room you can Hijack the Stump and get a kill with it (2/4 Enemy Among Us)
Proceed, you will open a door an see the next enemy you are going to Hijack. Wait till the Pouncer jumped down and Hijack him and get a kill (3/4 Enemy Among Us)
Clear the Area, then you need to defend the area. In the first wave the last enemy for the achievement appears, the Elite Hunter (invisible/cloaked Torque Bow Drones). Hijack one , let him kill a drone and you are done. (4/4 Enemy Among Us)