Idle Champions of the Forgotten Realms

I was able to unlock this about 3 weeks after starting the game with a mix between some fairly active playing and idle time of only checking in once or twice a day. If you do plan on playing the game for a bit and trying to collect other achievements this should just come naturally.

If you just want to focus on grinding out the kill achievements (which isn't necessary if you are playing the game regularly) you can turn off auto progression and stay at an early level where you one shot all enemies and set it so your xbox does not turn off.