how do i transfer between 121 & 89?

ok well the cb of 121 is 114 ftp and the 89 is 89 and the only method of transfering i know of is bh and ide use that but cant get in the same crater. ide either need a lvl 95-100 or some other method of transfering, ive heard of people talking about d stones whats this? and its like 10m so i dont really want to do party room.