The defending player may block Tromokratis with each creature they control. If that player can't, perhaps because one of those creatures is tapped, or chooses not to, Tromokratis can't be blocked.

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.