SCT Controller reported issuing a descent that led to an aircraft flying below the next point of the STAR; and below the MVA earlier than normal.

Narrative

Aircraft X was descending via the DSNEE STAR. I had IFR traffic that the STAR would not ensure separation from. Because of this; I needed them to descend now; below 7000 ft. Typically; in this situation; I don't even use the STAR; I just issue manual descents all the way until the bottom of the STAR; 4000 ft. For some reason this time; I said; 'Descend now to 6300 ft. (MVA) then descend via the DSNEE to 4000 ft. They read what I said back. When aircraft descend VIA the DSNEE; it often takes them below the MVA. So me seeing them below the MVA did not trigger concern. When I looked at them again; they were level at 4000 ft. much earlier than they normal would be. That is when I got scared and analyzed the descent. It dawned on me that while I descended them to 6300 ft.; it put them below the next point of the STAR that they would have crossed at 6500 ft. Because of this; they descended directly to 4000 ft. This is not something that is talked about. I am familiar with 'descend now to XXX then descend via' clearances; but in this case I missed that the next point was 6500 ft.; most likely because I usually do not use it; which is my fault. Ultimately it is my fault and I made a mistake. It wouldn't hurt to talk about it because this is not something we talk about a lot."