can someone explain boss resistances

[pulse37]

so ive been trying to understand how boss immunities and resistances work, and what level resistances bosses have in general.

I read somewhere the -phys and-magic kind of work like an aura for yourself, lowering the resitances of bosses.

But how much do i need? Do i need an amp + the -phys to peirce?

I heard mappo has 250 physical resistance, would i need 250 to pierce it then? or 260 to start doing damage? or do I need an amp on him + the -phys on gear?

also whats the resistances of the end game puzzle bosses trag and ctoggha? I know they cant be cursed with amp, so is it possible to actually kill them with just phys?

i would appreciate if any veterans can explain this to me!

[LordManhammer]

Amp damage, the lower resist curse, and the conviction aura all work at 20% efficiency against immunities. Meaning that if it says "reduces monster resistance by 100%" against an immunity, they only reduce by 20%. Usually this is enough to "break" the immunity and then you can start doing damage. Some bosses here have higher immunities than normal D2 bosses. Phys, magic, and elemental pierce on your gear will pierce immunities at full effectiveness though and will work against bosses or monsters that are immune without first breaking the immunity. That is unique to Annihilus.

You're probably better off using elemental damage against Mappo as 250% resistance is a lot to get through. From what I understand, you would need to pierce the resistance to below 100 before you can start doing damage. So Amp would give you -20% and you would need at least another -131% before you could damage Mappo with phys. I could be wrong though

[rrra]

So I am pretty sure that Mappo has 200 physical resist. Therefore, you would need 101 physical pierce to start doing damage to him. Ideally you would want 150ish. Remember that amplify damage and ssshaa's sword aura count for 20 and 4-5 pierce respectively when breaking an immunity.