Thrym stole Thor's hammer, so to get the hammer back Freya had to marry Thrym. They disguised Thor as Freya, and before the wedding began Thor was handed Mjollnir (the hammer), They returned to Asgard after killing Thryme.
Balder had a dream of him dying, which led her mother to make promises with everyone and everything, except the mistletoe. Loki who does not like Balder is on a mission to kill Balder, so he tricks his brother(who is blind) to shoot Balder with the mistletoe arrow.
Freya wore a beautiful necklace more beautiful then all, and Loki wanted it. Loki sneaked into her bedroom to snatch the necklace, he eventually got it, but Heimdall caught him and returned it back to Freya.