The boss system is a proposed system in which more powerful creatures would be randomly generated in a hunting area or used for events. Currently the plan is that only veterans would randomly spawn, all others would be GM triggered.
All boss critters will have a flat-chance to fail RETREATing from. This chance increases with the boss tier and the number you hve engaged with you. FLEE is always an option, assuming you can survive the roundtime.
The to-hit bonus works both ways. Champions more easily hit players at all skill levels, but are also more easily hit by players of all skill levels. In this way it encourages group hunting within about a +/-25 to 50 circle range, depending on the boss level.
Minion - bog standard critter
Veteran - has seen a number of battles and can take a much larger beating than normal. This monster has a higher base to-hit, and is a bit easier to-hit across all skill ranges. Soloable, with some added risk.
Champion - a stout master of many victories. The champion has damage resistances and an extraordinary to-hit bonus - both of which can be brought down with combos. Without the innate to-hit bonus, the champion is still going to land and take more blows than normal. Limited CC resistance and minor health regeneration. Not recommended for soloing, a small group likely needed.
Elite - the highest rung of warrior. The elite represents the pinnacle of strength and combat capability. Elite enemies will generally be a stronger version of the champion with moderate health regeneration and special attacks to boot. A large group is recommended.
Unique - these will generally be "Lyras" level enemies. Much stronger than Elites. Not always intended to be killable by a large group without resorting to tricksies.