The new types of giants could be fire and frost/ice they would have weakness to fire and ice arrows or swords They could be some kind of new boss monster or just a training monster, Now if they were used for training I am not sure on the best level for them as it is hard for the Pro's to train on giants or so I have heard, Could be around 150~155 A/D in that range again i am not sure if they could be trained on at that level.
As for Invasion/Instances boss they both again have a weakness to fire and ice type weapons/arrows they could have around 5,000health to 10,000Health and have a drop kind of like mare bulangiu or something around that.
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They could also have chance or Do fire and ice damage.
Ice/Frost Giant could have a ability paralyze a opponent when being attack.
Fire Giant could have the ability to burn an opponent would be like poison and do damage overtime.
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This is just an idea i had when i was talking to some friends, I know i will get some who may disagree with me.