Here is the full list of all 15 Guardians of Middle-Earth trophies - there are 13 bronze, 1 silver and 1 gold.
Win 25 total Battlegrounds Matches
Earn 20 Guardian Kills in any single Battlegrounds Match
Earn 50 Accolades total in any Battlegrounds matches
Win with a Tactician-Class Guardian in any Battlegrounds Match
Win with an Enchanter-Class Guardian in any Battlegrounds match
Earn 5 Accolades from any single Battlegrounds Match
Win with a Striker-Class Guardian in any Battlegrounds match
Use an Ultimate Ability to defeat an Enemy Guardian in any Battlegrounds Match
Win with a Defender-Class Guardian in any Battlegrounds match
Kill or Assist a Guardian from each Class once in any Battlegrounds Match
Win with a Warrior-Class Guardian in any Battlegrounds Match
Earn a combined Guardian Kill/Assist Streak of 8 in any Battlegrounds Match
Capture 15 Shrines total in any Battlegrounds matches
Reach Level 14 in any Battlegrounds Match
Fall on the Battleground