If another effect (or effects) modifies how much damage your Giant source would dealby preventing some of it, for examplethe player being dealt damage or the controller of the permanent being dealt damage chooses the order in which any such effects (including Calamity Bearer's) apply
The Legendary Birds alone make this set worth exploring, and the prehistoric lineup of Aerodactyl, Kabutops, and Ditto give it a personality that no other early expansion can match
Some examples include Teferi, Time Raveler, Omnath, Locus of Creation, and Fires of Invention
Combine this with goblin tokens and a card like Rundvelt Hordemaster, and you can cast a good chunk of your deck
King Dragun X DARK Level 7 [ DragonFusionEffect ] ATK 2400 DEF 1100 "Lord of D." + "Divine Dragon Ragnarok" Your opponent cannot target Dragon monsters with card effects
On top of that, the card is also a stellar combo enabler, with Ygra, Eater of All in particular