Up to a point, the BK117 sloping ground landings are "normal". The trick is to know when it stops being normal! 8 degrees all round, with 11 degrees when sloping to the left, and 5 degrees if the MMI is U/S, are the book limits, but cyclic trimming to keep the rotor disc level can have an impact well before that.
Above 5-6 degrees, some caution is needed, and at or near the limit, there is a very good chance that the MMI light may flicker. If it goes on and stays on, apart from an inspection, there is a reduction of 100 hours off the remaining life on the MGB bolts.
On extreme slopes, I accept a "collective" landing or take off, with little cyclic input once past about 5 degrees of trim: messy, but a bit of skid wobble is far better (IMO) than pinging the MMI. If the MMI gets into the yellow, and there is still a degree or two of slope left before both skids are on the deck, leave the cyclic trim, just lower the lever and accept a bit of slip from the skids.