What build/strategy did you use?
snowtree root(tri), any shield, treefiend entrails(3 casts), sanguine cannon, vimblossom fruit, and spear fragment(you don't need this to beat him. i was just being greedy for points).
try to get counters, elemental weaknesses, and save/sacrifices on the mobs leading to Cerberus for points.
before i trigger spawn i took my health down to black rite with sanguine cannon, and then planted/ ate vimblossom fruit. when you trigger the battle press start to skip the sequence and plant the treefiend. what i was doing before was standing behind the golem. don't do this. the best way is to stand front-left or front-right of the golem. that way when Cerberus runs at you , you use your shield to bounce him back right in front of the golem. when you do this once and he's laying cancel your shield, and start tapping your snowtree(don't charge it) until he freezes. then unleash a new golem before the first runs out. while the golem is whaling on him use your black rite. depending on what parts your golem hit, or curse spots he broke you could be done. if you aren't don't panic. he'll be red and pretty slow so just dodge his attacks until he runs at you. at this point you can either let him fall on his own and attack with anything you've got or use shield to knock him down yourself and attack with anything you've got.
you may have to use the shield a couple extra times in between those steps to get him in front of the golem. and sometimes when the battle starts he'll do his ranged attack instead of running at you. if he does this walking to the side and dodging 2 attempts usually gets him to run at you.
i believe that's everything. good luck!