How do I beat solidum, telethia assassin in the tomb?

I was overlevelled during the fight but found it somewhat challenging myself. first off, leave the assassin alone. have everyone focus their attacks on the telethia and use chains whenever possible. my setup was shulk, reyn, and sharla. you need a bulwark (reyn) to draw in attacks and take massive damage, a support troop (sharla), and a high damager (shulk). use slit edge on the sides of the telethia and backslash on its back for massive damage, usually around 10,000. if you start taking too much damage use light heal on yourself. be sure that is at least level 7. i HIGHLY recommend doing monster quests around the world, not only for free experience and armor, but to help explore regions and fill your collectopaedia. full sections in the collectopaedia usually result in mid level gems that highly boost armor and weapon stats. shulk is loaded with strength up II and III and has one arts stealth on the monado. give reyn and sharla high defense and give sharla very high ether.