Okay first off.
Taken From The Wiki -
“Some achievements are only unlocked for the first Monarch.”
This is one of them.
A friend of mine did this with me, we did it in three sessions.
At 30 lands visited, It popped.
Not 50.
o_0
We did another 3 lands to make sure his wouldnt pop, and it did not.
Oof. Have a friend, Beat all 5 islands, then make sure hes a good friend cause this will require two playthroughs to get for both people.
Not hard once all isalnds are beaten, just teleport to the dock and wait for the boat. GL!