1. Are there any findings which can possibly hint to the origin of Tantra in the IVC?
2. Which religions where practiced in the IVC and are there indications that the IVC had atheistic influences (esp. Samkhya)?
3. Are there any new discoveries about the Shiva/Cerunnos seals and is it right to suppose that it is depicting Shiva sitting in a Yôga pose?
Submitted by Christoph Dressel
1. I am not aware of any connection between Tantra and IVC. If you are interested in the topic you may like to look up Swamy Sankarananda book on this aspect. I must however admit that I do not believe in any such connection.
2. It is difficult to name the Harappan religion as the script has not been deciphered. One can draw some conclusions from pictorial motifs on seals , sealings and copper tablets and terracotta figurines of Mother goddess etc., I still think Marshall in his book on Mohenjodaro gives the best summary. While I do not Identify the Harappan religion with any of the modern Indian religions, I do think that many elements of the Harappan religion have been inherited by the later Indian religions namely Hinduism, Buddhism and Jainism.
3. I am not aware of any new discoveries of the motif. For the rest see my answer to Giuseppe.