Dead Trigger 2
Dead Trigger 2 is by far one of the best shooter games for mobile. Even if it's a few years old. It's no PUBG, but it isn't trying to be. It's a zombie first-person shooter with tons of missions, guns, and excitement. Not only is this game extremely entertaining, but the graphics are seriously impressive.
As long as you can handle some scary and stressful moments where hoards of zombies are chasing you, you'll love Dead Trigger 2.
While DT2 is an ever-changing game that gets updated constantly and has a multiplayer mode, it does work offline. Which surprised me, to say the least. Every update adds new content, so you'll never run out of fun.
So far, Dead Trigger 2 has over 33 unique locations or levels, 55+ weapons, 600 different gameplay scenarios and constant updates. Seriously, it's one of the best offline shooters, period.