combine question

if i combine a dark plus and a regular dark will i get a dark plus back or no if successful

You'll get a regular one

oh forget that

Any successful combine involving 0 or 1 plus monsters has a chance of giving a plus monster if combining for air, dark, holy, or earth. However, plus monster is not guaranteed unless successfully combining two plus monsters.

Not sure if using 1 plus monster has a better chance at a plus than using 0.

2 plus monster is 100% ?

No its not. I combine 2 earth+ ancients succesfull and only got an earth chaos not +

When the dark+ came out I special combined + and non plus twice and both times were successful but the third time it became a regular supreme there might be a slightly higher chance if you special combine but it definitely isn't 100%