Diablo III: Reaper of Souls

If you were to combine that with the Marauder set AND the quiver that allows you to have 2 more sentries out, that's one hell of an insane combo... too much RNG involved for it to ever happen though.

The Spike Trap/Caltrop/Sentry count from Helltrapper doesn't count towards your personal limit, so it can add more to the field than you normally would, but even with maxed out APS, you'd probably never have more than 4 extra Sentries if you were at a boss and shooting the whole time. It would be a decent item if I were to run places with high HP, since the extra Sentry damage could come in handy. Caltrops are useless since they spawn at your feet and elites don't give a pomegranate. Spike Traps do way too little damage too slowly to be worth the bar slot, especially for a Hand Crossbow, so if all three explosions hit, it equates to an average +14.4% Weapon Damage. You'd have to be partied with some good crowd control to keep a monster stationary for 6 seconds, and it would have to be pretty high torment for it to not die in the time it takes for Spike Traps to come out.

I have that thing. I think it's bugged. A lot of the time it'll drop one or even two sentries immediately when I move into a new map. :S

It seems to activate whichever skill it last procced for the next minute or so when you change maps.