The Siege Perilous is an artifact that allows the user to travel through alternate realities
In New Warriors, The Goblin steals the Siege Perilous from the armory in the S.H.I.E.L.D. tri-carrier and uses it to teleport away.
In the four part Spider-Verse episode, Goblin uses Electro as a power source for the Siege Perilous and uses it to travel to different alternate realities to take blood samples from alternate Spider-Men. Spider-Man would then use the Siege Perilous to summon the alternate Spider-Men he met while chasing Goblin to form the Web Warriors. After defeating Electro, Spider-Man would then use it return the alternate Spideys back to their reality.
In Miles From Home, Doctor Octopus and Baron Mordo would use the Siege Perilous to summon the Goblin from the Ultimate Universe. Goblin then attempt to use it to destroy the reality only for Miles to destroy it with his venom blast power.
In the four part episode Return to the Spider-Verse, Madame Web and Nick Fury informs Spider-Man and Kid Arachnid that by shattering Siege Perilous, fragments of it were scattered across the multiverse. They then warn them that the Siege Perilous fragments would caused all the dimensions to collide against each other if they are not collected. Doctor Strange and Madame Web, sends the Spider-Men through the multiverse to gather the fragments and ends up in Blood Spider's dimension. After finding one piece of the Siege Perilous, Blood Spider attempts to use it to destroy all the vampires for good, but ends up getting captured. The Lizard King then uses it to block the sun. In reality, Wolf Spider, who is originating from another dimension where he is completely evil has his own agenda to collect the shard, rule entire universe and absorbs the life force of the good Spiders. Spidey and Kid Arachnid are still looking for the shards of the Siege Perilous to find, until it ends in Arachnid's home world where Spider-Gwen takes his place when he was stranded in the mainstream universe.
In Strange little Halloween revealed that Siege of Perilous also has a power to seal the person inside of a universe, as what happened when Ultimate Goblin use it on Baron Mordo and when Wolf Spider overloaded the Siege Perilous when he absorbed the powers of all of the good Spidermen and Spiderwomen. However, Mordo managed to escape when he found the Microverse which was in Ant-Man's lab. He then used the fragment of the perilous to transform people into their costumes including Ant-Man. He then baited both Spidey and Strange, as well as a now cured Ant-Man to get back to mainstream world. Though Mordo succeeded and managed to use his new reality bending powers to change reality and transform buildings and cars into monsters, Spidey, Dr. Strange and Ant-Man to use their imaginations to counter Mordo's spells and trap him back into the Microverse once more.