"Plot twist" - hijack an enemy vehicle that have earlier hijacked you.
"Last resort" - melee kill an enemy while having no ammo left
"Bullseye" - perform a direct hit with a rocket launcher
"Party pooper" - kill an enemy player while he achieves at least an overkill
"God of nipples" - stuck an enemy player from a long distance
"Hoowayah!" - perform a ninja kill (jump above an enemy behind you and melee them)
"And what if you miss?" - headshot an enemy player while having extremely low health
"Phantom" - kill 3 enemy players in a row without getting shot at all, using active camo
"Who you gonna call?" - assassinate an active camo user
"Totally on purpose" - snipe an active camo user
"Immortal" - survive 5 shield breaks without dying
I like a lot of these, I would vote for the names on some of them. Some new concepts here I haven't seen or thought of myself, namely, "last resort", "bullseye", "god of nipples" (what is that name ha, great idea though.) A long distance stick is more than a hail mary, and its own thing for sure.
Party pooper can just be "kill joy" returned from previous halos, where you end a killing spree of at least 5 or more.
I would call Hoowayah, "Cowabunga" instead.
"immortal" is already "hard target" I believe.