SCT TRACON Controller reported descending an aircraft to an altitude below the MVA resulting in flight towards terrain. The controller issued an alert to the aircraft.

Narrative

I was working 4 aircraft into SDM (3 jets and 1 small aircraft; higher volume than normal) and the weather had lowered to BKN030. I advised the pilots that a few aircraft had gotten the field in sight for the visual before the weather had decreased. Due to the updated weather; they were being vectored for the RNV 8L. If they got the field in sight; advise me. The MVA to the east is high; so generally when aircraft see the field late and are cleared for the visual approach; they overfly the field to enter the north downwind. Aircraft X was the last aircraft in the conga line. Once the third aircraft was over the field and below 030; I initiated a descent for Aircraft X to 040. I worked a few other aircraft; looked back and realized I had descended him in a 050 MVA. He was a foreign pilot. SInce it was my fault; I advised the pilot of this before I issued the low altitude alert. In my apology; I didn't issue 'check your altitude immediately' in the phraseology.Suggestions: In the future; I'll issue the correct phraseology to fix the issue and then apologize to the pilot. I have been here for 15 years and am very careful with MVAs. I got zoned in on getting the aircraft lower to get the field in sight. I should have just handed this last aircraft off to the adjacent sector; so they could work him in and get him lower in an appropriate time.