[Taqwus]

Skull talisman is nice and extremely cheap. For similar reasons, it's hard to assassinate death mages -- the cheap battlefield summons. And be careful with feudal leaders, as it's not uncommon for even a priest to have one or more heavy cavalry as bodyguards...
Star children make nice assassins because of the prec-100 mindbLast, but against a leader with fast bodyguards or that can summon troops, they have problems.
Spirit helmet or phoenix rod are nice but very expensive. Boots of quickness = good combo with items that require action e.g. phoenix rod, skull talisman.