What could be some teachings that Buddha has not revealed to us? In Maha-parinibbana Sutta Buddha has said:

&quot;there is nothing, Ananda, with regard to the teachings that the
Tathagata holds to the last with the closed fist of a teacher who
keeps some things back.&quot;

however, in Simsapa Sutta Buddha says:

&quot;there are many more things that I have found out, but not revealed to
you. What I have revealed to you is only a little.&quot;

Do we have any knowledge about the teaching that he has not revealed to us? The commentary on accesstoinsight writes, &quot;This famous saying has been taken to justify the doctrines of various Mahaayaana schools, Theosophy and so on.&quot;
Could that be the teaching of tantra? I hope there's some good insight here.
Yes,  of-course buddha hid lot of teachings.  They were mostly related to superpowers like how to use capability of  brain to control others,  flying,  instant-transmission,  preaching to deva-lokas,  teaching in future(time travel) and what not? 

Alas!  It was all for nothing as later on various tantriks at nalanda university were probably having advanced knowledge on all this and for goodness,  it was burnt down otherwise today would have been worse in terms of black magic,  sex-tantrism,  immoral monks and much more. 

These type of teachings were never required and have nothing to do with attaining nibbana.