that set sucks. im sorry.
u never use one turn charging moves like hydro cannon
and u dont ever use quick claw.
also, why would u run a mixed set when his special movepool is enough for the job?
ice beam surf grass knot (i think) and with hidden power, it gives u great coverage.
the ev also sucks
The set definitely can be worked on, but it doesn't mean you have to put them down for it. Maybe this person is new to competitive battling? I don't think anyone likes being shot down when they're still learning.
But regardless, bluemon does have some viable points. Mix Empoleon may be surprising, but you really only ever see Emp with either a solely Physical or solely Special set. Hydro Pump/Surf is its best choice for Water STAB, and Ice Beam with Hidden Power work well for coverage too. Also if you're running a more defensive/supportish Empoleon, Scald may be used.
Really it all comes down to what kind of set you want to use. Empoleon is versatile enough to run an unconventional spread, but for items you'll probably want to go with Leftovers, or even Air Balloon, if you fear being hit with SE Ground type attacks. Life Orb is also viable if you want to go offensive.
And for EVs, again, this depends on the set you wish to run. If you'd like to stick with your Mixed Emp, you should go with:
(Idk about the EVs, it depends if you want Bulk or Speed)
-Drill Peck
-Earthquake
-Hydro Pump
-Ice Beam
And Life Orb, Lefties or Air Balloon as your item.
Good luck with your set!