The Leviathan are colossal monsters that function as both warships and assault crafts for the Chitauri army. They are an original creation of Zak Penn and Joss Whedon and resemble the Midgard Serpent, which are a recurring villain in the THOR comics and are often seen in service of Loki.
The Jotunheim Beast is a gargantuan animal native to the home of the Frost Giants, Jotunheim. They can be frozen solid for extended periods of time and run at incredible speeds. Only two have been seen, the first was awakened by Laufey to kill Thor, Sif and the Warriors Three on Jotunheim. The second was disturbed as Malekith and Thor battled through different Realms during the Convergence. The beast eventually landed in London and rampaged the city for at least two days.
The Abilisk was an enormous multi-dimensional being that fed on power sources. The Abilisk was able to travel between dimensions, posses superhuman durability and could shoot rainbow colored trans-dimensional matter from its mouth. The Guardians of the Galaxy were hired by The Sovereign to fight the Abilisk to prevent the beast from from devouring the Anulax Batteries. The Abilisk is an original MCU creation but the Guardians of the Galaxy’s first mission in the comics was to prevent an inter-dimensional beast from breaching the universe through a fissure in the space time continuum. James Gunn, the director of GUARDIANS OF THE GALAXY VOL. 2, described the Abilisk as both “a naked pink mouse” and “the inside of an old man’s ear”.
The Fire Dragon was a gigantic dragon native to Muspelheim, the domain of Surtur and one of the Nine Realms. This beast could fly and presumably breathe fire. After a brief fight and chase with Thor, the Fire Dragon is beheaded by the Bifrost Bridge.
Fenris was an Asgardian wolf that was loyal to Hela and fought alongside her as Hela and Odin conquered the Nine Realms. Fenris stood 23 ft. tall and possessed enhanced sense as well as incredible strength and durability. When the conquering was done and Odin was ready for peace, he imprisoned Hela and Fenris was put to death. Upon Odin’s death millennia later, Hela is released from Hel and resurrected Fenris with the Eternal Flame. Fenris’ second death came at the hands of the Hulk when Fenris was thrown over the edge of Asgard. During their fight, Fenris is able to pierce the Hulk’s skin and is only the second character in the MCU to do so, the first being the Abomination. In the comics, Fenris Wolf is a character of Asgardian descent, said to be the offspring of Loki and the giantess Angrboda, and is the brother of Hela. Unlike the her comic book counterpart, Fenris is a female in the MCU.