Hanzo's poison (Kazuzu is not immune to it) and Mifune's chakra enhanced sword which was on par with Sasuke's chidori enhanced sword (same chidori that effortlessly pierced Kakuzu while Kakashi used it)
Kakuzu is immune to hanzos poison. You need a standard circulatory system for poison to work in the first place, you breathe it in and it goes into your bloodstream through the capillary sacs (alveoli) in your lungs and spreads throughout your body via blood vessels.
Kakuzu has no blood vessels or a standard circulatory system. Due to his villiages tech, the inside of his body is just a mass of black tendrils, so there is no way for the poison to affect him.... plus even if it did he can easily blow it away with futon...
as for mifunes blade, that IS NOT getting through kakuzu's domo hardening. The only reason why kakashis chidori pierced it is because it is a raiton nature, which hard counters earth