This kanji is made up of the ground radical (which also happens to be the kanji for "one") and the radical for two. Combine one and two together and what do you get? Three!
Three is the number of chances you get with Santa-san (さん). He has a list, and when you get to three "naughty things" lines, that's it. You're on Santa-san's three strikes and you're out list.
Currently there are no similar looking kanji which exist in the WaniKani learning system