How does grapeshot interact with remand. I see it played in storm decks but im not sure why?
When you cast Grapeshot or any other spell with Storm, the Storm ability triggers and that trigger makes a bunch of copies of the original spell. That trigger and the copies it creates all resolve separately before the original spell does, and the original spell doesn’t need to be on the stack for them to resolve.
When you Remand your own Grapeshot, you’re putting the original Grapeshot back into your hand so that you can cast it again and benefit from the storm trigger twice. The copies created by Grapeshot will resolve normally even if it’s no longer on the stack.
For example, I cast Seething Song, Pyretic Ritual, and Manamorphose, ending up with URRRRR in my mana pool. I then cast Grapeshot. When Grapeshot’s storm trigger resolves, it makes three copies of Grapeshot. I then Remand the original Grapeshot to my hand and then recast it. When the storm trigger from the second casting of Grapeshot resolves, it creates five copies of grapeshot. All in all, 8 copies of Grapeshot and the original Grapeshot resolve here, allowing me to deal 9 damage with the spell.