Two general strategies, depending on resources at hand.
Option 1: limit mobility and wear it down from afar. Its size can be made to work against it
Option 2: debuff and pile on. As an example, I recently helped take down a brass golem with a simple level 1 spell, Grease. Cast it on its weapon to make the golem drop it, then cast it under the golem's feet to force it prone on most turns. I wish I could claim creativity in that regard, but the truth of the matter is the bloody thing was 100% immune to every other offensive spell I had.
Edited: daishain on 13th May, 2017 - 2:10am
Daishain,
Great strategies. I can also see a spell like Heat Metal doing wonders if the Giant is wearing some type of armor and/or is carrying a metal weapon. But sheer numbers is also a way to do it… but expect a lot of casualties. Some would be in support casting a firing while others attack head on.
Someone casts hold monster. The thief then backstabs, the magic users hurl lighting bolts, the Druid changes into a bear and summons more bears. Other melee fighters pile on. Game over for giant.
As mentioned earlier, it all depends upon level. At lower levels you run. At higher levels it isn't a challenge.
Edited: Kyrroeth on 13th May, 2017 - 9:35pm
Everyone is going all about it all wrong. Easy way is to go out on the ice. Cut a real large hole in the ice. Line the hole with peas. When the giant goes out on the ice to take a pea kick him in the ice hole.
Ok in all seriousness the best way to kill a giant is to fight him on your terms and not his. IF you can get him at a disadvantage that his size is taken away it is much easier to beat him.