Using a 'stiffer' material for a dropper tippet, IF it come off of the bend of the first fly's hook, will help lessen tangles.
If you need a 'long' dropper, say 12 to 30 inches, then the most 'non fouling' system is to tie the dropper tippet to the bend of the hook, or to a dropper loop built into the leading fly. This keeps the whole set up 'in line' and helps with fouling.
Anytime you extend a length of tippet at an angle to the main line, and it originates from someplace other than the 'bitter end' of the tippet, you are creating an excentric that can lead to tangling by it's very nature.
Some of the more popular systems use a set up where you have, in effect, two separate sections of tippet, one shorter than the other, leading to the flies (the type of 'knot' used is unimporant). This type of 'V' system leads naturally to both lengths of tippet twisting together during the cast.
Other systems where the dropper is tied to the tippet, or extends from the tippet, at any place ABOVE the termainal fly, also are prone to the dropper line 'twisting around' or fouling the main line. Shorter droppers can atenuate this, as can using aerodymanic flies that won't osscillate or spin in the air.
There isn't a multifly system that won't foul. Some can foul more, others less. A lot of it has to do with the casting skills of the user, as things like wind knots and tailing loops are magnified by the presense of more lines and flies.
Good Luck!
Buddy