YOU SAID:

my buttocks are larger than an elephant's crushing a dog's head with their mass

INTO JAPANESE

私のお尻は象が犬の頭をその塊で押しつぶすよりも大きいです

BACK INTO ENGLISH

My ass is bigger than an elephant crushing a dog's head with its mass

INTO JAPANESE

私のお尻は、その質量で犬の頭を押しつぶす象よりも大きいです

BACK INTO ENGLISH

My ass is bigger than an elephant crushing a dog's head with its mass