Consider

               == Difficulty Arrows ==
[[Image:Target 1up yellow.jpg|163px|right|thumb|This monster is as strong as one average level 40 character.]]
[[Image:Target 3up white.jpg|163px|right|thumb|This heroic monster will take 3 players near level 68 to defeat.]]
When you target a monster, it may have up-arrows or down-arrows in the target window. The arrows indicate how powerful it is ''for its level''.  Here's a simplistic way of understanding the difficulty arrows:
# A ▲ one-up-arrow mob is an even match for 1 average player of the same level.
# Each additional ▲ up-arrow means you need one more player to fight it.
# If there are no arrows, or ▼ down-arrows, then the monster is weaker than a player of the same level.
# Sometimes monsters are grouped together into an "encounter".  In this case, the total difficulty comes from adding up the arrows on all of the monsters in the encounter.
# The game automatically uses the label "Heroic" on any encounter that adds up to ▲▲ two up-arrows or more.
# The game automatically uses the label "Epic" on any encounter that adds up to six up-arrows or more.

Of course, you can improve your chances by using better gear/spells, or by having a higher level than the monster.  Either of these scenarios lets you double the number of up-arrows that you can handle.
{|
|
▼▼<br>
▼<br>
even   <br>
▲<br>
▲▲<br>
▲▲▲<br>
|
= 1/4 as strong as a player<br>
= 1/2 as strong as a player<br>
= Good match for a player in poor gear and Apprentice spells<br>
= Good match for a player in average gear and Adept spells<br>
= Good match for 2 players<br>
= Good match for 3+ players<br>
|
|}