Mind Blank and See Insibility

[sirmaniak]

Hi. I have some doubts about the Mind Blank spell. Three Annis Hag have casted Mink Blank and Invisilibity on themselves. A PC has the spell See Insibility. Do the three Annis Hag need a saving throw in order not to be discovered? What is the DC?
Thank you.

[LordKailas]

So far as I can tell mind blank directly blocks see invisibility. No save or skill check is involved at all.

[sirmaniak]

Thanks :)