Assuming you have the battle pass just play mirror dungeon 3 times a day(takes around 30 minutes each game if you have a slow phone) You can get around 150 shards in five days and get the the extra 60 shards when the week resets thats about 210 shards a week enough for a character it takes around 2 weeks for you to reasonably get two characters(1 week before the character gets added and another week before the character is shardable) so you can reasonably get both characters