Tromokratis has hexproof unless it's attacking or blocking.
Tromokratis can't be blocked unless all creatures defending player controls block it. (If any creature that player controls doesn't block this creature, it can't be blocked.)
2/1/2014 The defending player may block Tromokratis with each creature he or she controls. If that player can’t, perhaps because one of those creatures is tapped, or chooses not to, Tromokratis can’t be blocked.
2/1/2014 Tromokratis (like all attacking and blocking creatures) remains an attacking or blocking creature until the end of combat step is over. Notably, it will still be an attacking or blocking creature during the combat damage step, so any abilities an opponent controls that trigger when a creature dies as a result of combat damage could target Tromokratis.