You can get the Exotic Mentor bounty from any bounty turn in. The more Bounties you turn in at once gives you more exp/reputation per bounty and seems to give you a slightly higher chance for a mentor bounty. Also, you can get the exotic bounties from turning in Eris bounties as well, adn I assume that would be true for Crucible and IB bounties. The basic idea is that you pick 3-5 easy to do bounties an evening and just do those. Look for bounties that synergy well, like 100 kills without dying and 9000 exp without dying and 100 precision kills. Or Fallen Leaders + venus patrol + super kills (Venus has a great spot in Ishtar cliffs to farm Fallen or Vex majors + super kills, also ember caves loop). Another example is Mars patrol, cabal/vex leaders. Etc. Knock out the Eris bounties on teh moon or earth replaying the story missions. Good luck.