Killy RM is by far the most fun RM build to play. I can occasionally do the standing still thing on another mech, but really it's Killy or nothing for me. I held off on this too for a long time but nothing earns more/faster in Tournament for f2p & low spenders than this build, so go for it!
This thread has a ton of great tips and helped me a lot:
war-robots-forum.freeforums.net/thread/46072/kinda-suck-rocket-mortars-adviceMy best tips:
* Radius implant is the most important and the gold one comes up in the store. Make sure to buy and max it when it becomes available. Damage is next and you like won a purple one already. Range is useful but the lowest priority of the three.
* Use the mini-map to aim and aim for groups as much as possible. Target the lead bot in whatever direction the group is moving. Focus on this especially in the beginning of a tournament match when reds all start from the same place, but wait a few seconds to see where they head and who's in the lead.
* Target frozen and fully slowed reds for easy kills.
* When targeting a human player, it's best to wait until an AI is standing near them and to target it instead. Usually they won't get an incoming rockets warning when you do this. On a bunch of maps when you can't see where the human is, it's often worth it to target AIs when they pass by likely hiding spots and see if you get hit icons from more than just the AI. Also, FYI, when you're up against human RM players it is best to stay away from your teammates for the same reason (and also because groups are the targeting priority).
* Generally limit shots to 120m or less. Closer is better because there is less hang time but it comes with more risk. Two good maps for this in particular are Agora (shooting from the ramp on the middle structure) and Tunnel of Fate (shooting from the side a bit behind the midpoint). One trick I like to use if it is in the final seconds of a match, is to hit the dash and then shoot so my rockets land before the timer goes out. Since the match is about over, it doesn't matter that you're more exposed.
* When going up against humans definitely keep an eye out for them. Surge players in particular will be heading right towards you. This is where the range implant comes in handy. Generally it's not worth it targeting Killshot RM players unless you do the AI-adjacent trick or have a second salvo ready to launch right after their dash (ditto Lancer players). But one trick is to target them when you see your AI teammates getting close to them. That will make them use their dash and flush them out to get killed by the AI.
* If you are up against a human who keeps shooting RMs at you even though they have seen you dash with your Killy, it can be useful to cruise around a bit and make them waste their shots. Just keep moving, save up your dash, and be mindful of getting near your AI teammates. While they waste shots on you, you can rack up kills targeting AI.
* Targeting mainly AI is often the best way to get the most kills and points. But it is good to take out a human opponent's first mech, especially if it is an RM setup. Regardless though it is likely to be their strongest mech so taking it out will help you win the match. Watch their next spawn though - often they'll beeline it right for you.
* Avoid targeting mechs too close to high walls. They block most of the shots and cause only partial damage. Over time you'll get a sense of where the good kill zones are on each map. Also be careful shooting from behind really tall obstacles and overhangs which will catch all your shots as well.
* Patience is worth it. Given the slow reload it is tempting to fire as fast as possible, but it is good to wait and see if reds head towards each other for multi-kills. Also since often you can't spot all the reds, it can be good to target just the one you see at choke points and other spots where the AI usually goes.
* AI Surges, Lancers and Killshots can move too fast to hit. It is best to prioritize the slower targets when you can.
Hope that helps. Happy Hunting!
PLUS 
While I have had the MR12 since Beta, I probably have less than 30 games on it. It was never my style. But many have had great results on Killy, and I'm currently 5-7 and only need about 1000 A-coins to clone it. Going to be a learning curve, but camping with RM's isn't an option for me.
