Just use 2x damage and then wind-up punch then you will punch him to space.(LiftOff+Up'n'Away)
Go deathmatch and then set to anvil only at infinite ammo(easier)1 on 1, after mashed him, his anvil will drop, drop yours then pick the enemy's, use it to kill. (Recycler)
Go deathmatch then set 4 1337 bots to teammate and 1 noob bot to enemy team. Get the plunger and your teammates will take care of the rest. (Take the Plunger
Make a map where you will get an advantage of others. Use this if you want WINNER,1,null,8,$90;500;200;3,234;496;200;3,379;495;200;3,546;495;200;3,648;495;200;3,730;495;200;3$20;538;150;3,0;74;150;3,4;191;150;3,775;20;150;3,217;499;150;3,235;383;150;3,251;248;150;3,22;377;150;3,2;227;150;3,233;440;150;3,232;553;150;3$97;24,719;273,729;464,696;397,691;439,718;346
Settings : spawn with weapons, noob bots with all againts you, 2x damage.
Right after the game starts, shoot then shield your self. Voila ! you got yourself a 5x multikill. (3x,4x,5x multikill achievement) Reduce bots to get 3x/4x multikill if you're not lucky.
DOUBLE Jump away from a map, then use the sideswipe technique (press z & x simultineously while directing to a platform. Mind that you need high place at the jump off.(Zero Gravity)