If the spell has any targets, you may choose new targets for any of the copies." As the replicate triggered ability resolves, you'll copy Shattering Spree for each time you paid its replicate cost, even if the original spell is no longer on the stack at that time (perhaps because it was countered)
As is usual with these sorts of cards, many players will try to build decks with them but they'll never really end up being that playable in the face of a wider meta
How do we rank the best of the best
Following her floods, more rain came, then frogs, then sun and greenery
Glissas Retriever is both a finisher (since is has haste, toxic 3 and evasion from creatures with power 2 or less) and a grave recursion tool on death trigger with the potential to return up to 3 target cards (if we spread enough poison counters among players, which is not hard for our deck) Nim Deathmantle is a part of the infinite combo described above, but even alone, it is a nice grave recursion tool that gives +2/+2 and intimidate which is very powerful on a deck with creatures with infect and powerful EtBs
Summary Rakdos decks in Magic: The Gathering are aggressive and focused on damage, making them polarizing for players