Some trig can get ridiculously hard, there was one question in our yearly which about 3/190 people doing mx1 got full marks for, and it was a trig question combined with something else, can't remember now.
I struggled on parametrics for a while, but a lot of rigorous routine will make it click, and if you do 4u, doing locus in complex numbers makes parametrics look piss easy...
Perms and combs were okay, some things you have to know about them are weird, but once you understand it it's not too bad.