"Mind of a child, strength of three grown men. I've seen a half-giant tear the walls out of a building because he wanted a better look at the tattoos on a mul inside. - Daro, human trader
Legend holds in ages past a sorcerer-king or queen used wizardry to beget a union of giant and human to make a race of powerful slaves. Whatever the truth, the half-giant race has thrived, able to reproduce with one another, and are sought out as gladiators, soldiers, guards and mercenaries across the Tablelands.
Because of their artificial origins, there is no half-giant culture, tradition, or homeland. They readily imitate customs and cultures of those they admire or associate with. They are very imitative, eager to fit into a world that is not built for their size. One observing a dwarf quarry might watch for a time and then try his hand at it, moving on if he does not excel at it. Many find they excel at breaking bones and imitate those who are also skilled at this practice.
Half-giants are enormous individuals, generally 10 to 12 feet high and weighing in upwards of 1600 pounds. Though they have human features, these tend to be exaggerated in some ways. Skin tones range from light brown to deep tan, like sand. They vary in hair color and tend to wear whatever style or fashion they are currently emulating. Absent that, their giant heritage makes for thick hair amenable to braids. There is no economy for half-giant stature, so their clothing would likely consist of several human sized articles of clothing stitched together. A tavern would charge extra for filling enough plates for a half-giant sized appetite, and any armor would have to be specially crafted. Most nobles, templars, and merchant houses feel the investment is worth the return when they have 1500 pounds of enforcement at their command.
The most powerful warriors on Athas, half-giants seem content to dwell in humanity's shadow and drift towards charismatic leaders of all races. For example, if a half-giant village is near elven raiders, they are likely to emulate the guerrilla tactics of the elves. However, this innate need to fit in is more than a whim. It is inherent to the half-giant's creation. A half-giant farmer's village might be raided, and he may soon adopt the morals of the invaders because they seem to know what they're doing, and the half-giant finds he's pretty good at smashing heads too.
One axis of a half-giant's alignment will be fixed and the other subject to change, even daily, based on influential events or persons around you that you find a reason to emulate or admire. You will try out their morals or philosophies and perhaps stick with it for a time if you're good at it. This does not mean half-giants are unreliable - the influence must be strong for them to change, and they have a core philosophy that is fairly unchanging. A half-giant soldier might see a dwarven cleric of the sun and be impressed by her unflappable devotions. He may try shaving himself and praying to the sun until he finds he cannot stare at the sun without hurting his eyes and cannot make fire appear.
Half-giants inherit a solid balance of their bestial and human parents.
Ability Score Increase: You have 4 points to split between your Strength and Constitution scores. Your Strength score may reach a maximum of 22 instead of 20. Your Intelligence and Wisdom scores are decreased by 2 each
Age: Half-giants mature around 24 years of age and can live up to 220 years.
Alignment: Your alignment may fluctuate as described above in Alignment on a Whim. you begin with one fixed alignment axis (good-neutral-evil or lawful-neutral-chaotic) that will never change. The other axis may change depending on who you are emulating. Subject to DM approval, when imitating a charismatic leader, select an appropriate Ideal or Flaw and replace your current one. If the new Ideal is tied to a non-fixed axis of your alignment, change that aspect of your alignment.
Size: A typical half-giant stands 10 to 12 feet tall and weighs 1600 pounds. You occupy a 10-foot by 10-foot space and have a 5 foot reach. Your size is Large.
Speed: Your base walking speed is 35 feet.
Giant Body: You cannot wear ordinary gear sized for smaller creatures such as boots, gloves, and rings. All clothing, armor, meals, and lodging cost double for you.
Large Hands: You may wield normal sized versatile and two-handed melee weapons with one hand.
Colossal Endurance: Your immense body mass allows you to occasionally shrug off injury. When you take damage, you can use your reaction to reduce that damage by your Constitution score. You may use this once per long or short rest.
Giant's Toughness: Your hit point maximum increases by 2 and it increases by 2 every time you gain a level. You may stack this with the Toughness feat.
Languages: You can speak Common. Your voice is always low, making it difficult for most to hear and understand more than a rumble.
Large creatures require four times the daily amount of water and food needed for a small creature (DMG p111).
Magical gear adjusts for the size of the wearer from small to large. A half-giant or halfling can wear the same pair of boots if magical, but ordinary kank leather boots sized for a human simply won't fit.
Always remember how much bigger and heavier you are than everyone else. Take advantage of your height in combat, but remember the disadvantages. Between your size and your lessor wits (even if you are a relatively intelligent half-giant, people will assume you to be dull), you find yourself an object of comic relief. You are used to being teased and will endure more witty remarks than most people, but when you have been pushed too far your personality can suddenly shift, and you can unleash astonishing violence on your tormentors and any who stand in your way. Less frequently, these shifts can happen to you without provocation - you just wake up with a different ethos and altered disposition.
Remember you are influenced by powerful personalities, and can shift your personality and ethics. You tend to imitate the tactics, clothes and demeanor of your "little master."