Last Prism

Last prism is a drop from the Moon Lord. after (approximately) 4 second charge up during which time damage is still dealt but it will not deal as much damage as when it is fully charged.

There appear to be 6 beams that deals damage that rotate and get closer together as the beam charges, this takes aprox. 4 seconds, each beam does damage once per second. This means without crits or damage amplification this weapon does 600damage per second when fully charged. However due to the high mana cost (12 mana 6 times per second when fully charged is 72mana per second) players will struggle to maintain the beam for more than 5-6 seconds a Mana Flower is necessary for this weapon The beam does not pass through blocks but can pass through platforms.

Trivia
The life form disintegration rainbow may relate to the MOBA game League of Legends, where a champion, Vel' Koz has an ultimate skill called "Lifeform Disintegration Ray."

Or maybe from bullet hell game Touhou Project, where character Kirisame Marisa have Spell Card "Love Sign, Master Spark" that looks like huge rainbow laser beam that deals massive damage.