The papers you get, by the lot's route
What you need for the transfer depends on how the seller holds the vehicle, and the lot prints it under The papers for the transfer before you bid.
From a registered owner: the RC, the sale letter, the gate pass, and Forms 29 and 30 signed by the seller. From a lender: the RC it holds, and a fresh RC in the lender's name (Form 36) or the lender's own Forms 29 and 30; under SARFAESI, the certificate of sale the lender issues on payment. From a lessor: its sale letter and NOC. From a government seller, you file Form 32 at the RTO within 30 days of taking the vehicle. Under an order, the officer's sale certificate and a copy of the order. A machine never registered has no RC to transfer.
The same list appears in the tracker's transfer step and in the papers pack, so nothing is a surprise at the RTO.