War Mage: Eventide Ramparts. With the right barricade strategy, you can funnel all minion under the three cauldrons near the rift room. I get 500 to 600 enviro kills per run this way and its real easy. Obviously, you will want to use a range hero to shoot the cauldrons.
Falling folly: line the bottom lane with push traps, And use flip traps on top lane to throw the minions down to bottom. I'm not sure how many kills this will get you a match though