Plant Abuse Chart - 420 Magazine
Marijuana Plants Problems - Yellow Leaves, brown spots, nutrient shortage etc.
Cannabis Headquarters - Cannabis Plant Nutrient Deficiencies (with pictures)

I can Google too- you can find and cut/paste it, but I don't think you actually recognize it- this is NOT enough information to say 'you have an Mg deficiency'.
"my leaves tips are rolling down and some are canoeing,....Now some lower leaves are showing some discoloration....all of a sudden they look like crap,"

Leaf tips rolling down, canoeing. Could be excessive N or water, or rootbound.
Low leaf discoloration (discolortion NOT described any further as to WHAT color or pattern it shows). Could be overwater, aging in flower, insufficient light, nute lockout, N deficiency.
Plants look like crap. Could be they were eaten by the cat, thrown in the rubbish by Mom, tipped over, stepped on,....

Just illustrating- don't make a firm diagnosis on such shaky description. Those charts are only so helpful, when it's the CAUSE of the problem that is more important than what is specifically being locked out.