5e Monsters - Rune Giant

This giant’s skin is black and pitted, like roughly cast iron, and etched with glowing red runes.
Rune Giant CR 20+
LE Gargantuan humanoid (giant) - 40' tall
Init +0; Senses low-light vision; Passive Perception 21
Proficiency +6
Str 30 (+10), Dex 11 (+0), Con 24 (+7), Int 14 (+2), Wis 21 (+5), Cha 18 (+4)
AC 23 (Rune Plate)
hp 345
Good Saves STR +16 CON +13 INT +8 WIS +11 CHA +10
Resistance: cold, lightning, fire
Immune: Charm as long as their controlling Runelord is alive.
Advantage on saves against Banishment and other involuntary transportation (Plane Shift etc).
Speed 60 ft.

COMBAT
A Rune Giant may make 3 attacks using Greatsword & Javelin (2 only) in any combination, as well as a bonus action Spark Shower (if available). They typically open combat with 2 javelins of lightning, close in & use Spark Shower, then finish with one Greatsword strike.

Melee Greatsword  ATT +16 dam 45 slashing (crit 67 slasing on 19–20)

Ranged Javelin of Lightning ATT +16 dam 31 piercing (crit 46 piercing on 19-20) plus a 10'x60' lightning bolt extends 60' from the impact point doing 28 lightning (crit 56) damage to target, those behind target take 28 lightning and may make a DC 18 DEX save for half damage; javelin range 120'/360'; a SML target hit by the javelin is Pushed back 10' and must make a DC 25 STR save or be knocked Prone.

Space 20 ft.; Reach 20 ft.
Equipment: Greatsword, 2 javelins.
Special Attacks command giants, runes, spark inferno 3/SR

Spell-Like Abilities (Spell Save DC 18; Spell Attack +10)
At will—charm person; suggestion
3/SR—mass charm monster; dominate person
3/LR— true seeing; air walk

Skills Athletics +16; Craft +8;  Knowledge (history) +8, Knowledge (nobility) +8, Perception +11
Languages Common, Giant, Terran

SPECIAL ABILITIES
Command Giant
Giants (including Goliath) have disadvantage on saves vs  charm or compulsion effects used by rune giants.

Runes
Whenever a rune giant uses its spark inferno or spell-like abilities, it can cause the runes on its body to flash with light. All creatures within 10 feet of the giant must make a DC 18 CON save or be Blinded until the end of their next turn.

Spark Inferno (Recharge 5-6)
As a bonus action, a rune giant can cause a storm of sparks to erupt out of one of the runes on its body. These sparks function as a 30-ft. cone; 45 fire and 45 lightning damage; DC 18 DEX save for half (22-22)