Here is the full list of all 28 Knight's Retreat trophies - there are 8 bronze, 14 silver, 5 gold and 1 platinum.
Unlock all trophies
Succesfully retreat all the knights
Manage to retreat at level 70
Manage to retreat at level 66
Complete the nightime retreat
Make a untargetable path using the golden knight
Indirectly shoot the second type of pressplate
Use a troop to make a tile untargetable by your enemies
Manage to retreat at level 56
Complete the afternoon retreat
Manage to retreat at level 53
Retreat a group of two linked knights
Manage to retreat at level 50
Retreat two linked knights, but at different times
Retreat with three knight at the same time
Retreat with two knights at the same time
Complete the desert retreat
Indirectly shoot the first type of pressplate
Manage to retreat at level 27
Complete the daytime retreat
Retreat three knights on the same stage
Retreat two knights on the same stage
Complete a retreat in a stage with each variety of piece
Rearrange a queen to allow the retreat
Rearrange a bishop to allow the retreat
Rearrange a rook to allow the retreat
Rearrange a knight to allow the retreat
Start the retreat