Rogue Company

The easiest way I found to get this achievement was by playing as Saint on Strikeout game mode. When u start the match focus on leveling up your C4 to max so they are harder to see and you have 2. Next plant both of them on the site or a heavy traffic area. Then run to a zip line and simple keep going back and forth on it until someone runs into your C4.

Edit: Maps
Skyfell: two small zip lines on either side of spawn (safest and where I got mine) and a long one (high risk, in the middle of the map off to one side).

Falelas: one very short zip line in the middle of the map in the canal area. Probably not worth trying on this map because its so short, imo.

Windward: two long ones on the left and right. Both are on the side with the grassy courtyard drop area. This is probably the second best map to try due to the zips being in a medium risk area.

Icarus: no ziplines

I'll update with the other maps that have zip lines as I play.

*Zip On Lock* "Down an enemy while riding a zipline"

This achievement is pretty self explanatory down an enemy while riding a zipline.
you can get this achievement in multiple ways the two easiest rouges to do this on is
Saint or Ronin as they both have automatic detonators. if someone detonate it while you are on the zipline and you got the down for it you get it.

The best mode to get this on is Strikeout as its alot more easier when people have more than one life.

Camp a zipline and keep riding back and forth on it to find enemys its better when the zipline is near the objective. if you see an enemy on the otherside of the zipline try to damge him a little bit before riding the zipline than take it and try to down him while on it you can use your gun on it. some character like Anvil will switch to his pistol while riding the zipline so might wanna pick up a second primary
if you are not comfortable with your pistol

Ziplines are not on every map