Storm Giant

A storm giant on the party's side is a CR 13 oracle who happens to also throw lightning bolts. Chaotic Good and Wisdom 20 mean the giant probably sought the party out, not the other way around, and the alliance is conditional on the party serving a purpose the storm giant has divined from weather, currents, or sky-omen. Set that purpose openly and let the giant restate it whenever the party drifts.

In combat, the storm giant opens at range. Thunderbolt has a 500 ft. range at +14 for 22 lightning, plus the target is Blinded and Deafened until the giant's next turn. Use that on whatever enemy is currently controlling the battlefield: the enemy caster mid-spell, the archer commander shouting orders. Lightning Storm is the encounter-defining spike: 10 ft. radius, 40 ft. high cylinder, DC 18 Dex save, 55 lightning on a fail. Drop it on a tight enemy formation and watch the encounter pivot. Recharge 5-6 means the giant gets it back most rounds. Save Storm Sword (+14, 36 average per swing) for anything that closes to 10 ft.

The giant cannot be controlled by the party and should not behave like a hireling. They speak in pronouncements and they leave when their reading of the moment says to leave. Control Weather (1/day) is the campaign-shaping cast: clearing a sea voyage, bringing rain to a drought-struck farm, freezing a river so the party can cross. Make the party ask for it specifically and have the giant decide whether their reason is worthy. Lightning and Thunder immunity also means the giant walks through their own Lightning Storm with no concern, while the party must stay outside the cylinder; warn the players before they charge in.

Have the giant deliver one prophecy at the end of the alliance. One sentence, written down before session, that the party will spend three sessions interpreting wrong. The giant does not explain.

A hostile storm giant is a campaign-ender at most levels, so set the stakes accordingly. Maybe the party has broken a sacred storm-pact, maybe they killed a giant's beloved orca, maybe the prophecy required them to die and they chose to live. Sell the moral weight before initiative.

The fight runs at range, always. Storm Sword has 10 ft. reach, but the giant prefers to stand 400 ft. back and Multiattack with two Thunderbolts per round at +14 for 22 lightning each, plus the Blinded and Deafened condition stack. Two Thunderbolts on the same target Bloodies most party members in one round and locks them out of reactions. Lightning Storm on Recharge 5-6 lands on whatever cluster of casters or healers is the bigger threat: DC 18 Dex save, 55 average lightning on a fail, half on a success. Casters with low Dex die to the failed save.

Spellcasting is the difficulty modifier. Detect Magic at-will means the giant always knows where the party's magic items are. Control Weather pre-cast before the encounter buries the field in fog or drowns it in rain so the party can't see incoming Thunderbolts coming until they land. Truesight 30 ft. plus Darkvision 120 ft. plus Passive Perception 20 means the giant sees through Invisibility at close range and never gets surprised.

Storm giants do not flee easily. 230 HP behind AC 16 is a long fight, and Lightning and Thunder immunity shrugs off the obvious cleric and warlock loadouts. The giant withdraws only when its purpose is complete or when a Wisdom roll (which the giant will pass on a 5+) tells them the omens have shifted. If the party ever flees, the giant lets them go; storm giants do not chase.

Open the encounter with one peal of thunder, fifteen seconds before initiative, with no enemy on the map. The players should know they are being hunted before they see what.