Ancient Silver Dragon

A silver dragon on the party's side is the most generous high-tier ally in the metallic roster, which means the framing trap is letting it solve the campaign. It won't, because silvers prefer to teach rather than rescue. The dragon arrives in humanoid shape, often as a benefactor the party already knew, and it commits to a single named purpose: stop a specific war, recover a specific relic, witness a specific oath. Once that's done it goes home, because Teleport is on its 1/Day list and silvers value mortal agency too much to overstay.

In combat, run it patient. Cold Breath opens at a clean angle that excludes party members, which means you should ask the player positions before you place the cone. If the geometry doesn't work, the dragon takes a Rend round instead and waits for the cone to reset. Multiattack lets it swap a Rend for Spellcasting (Ice Knife, level 2), which is a low-cost ranged option for picking off a fleeing enemy without splash. Hold Monster at-will is your party-protective lockdown: name the enemy boss and let the cleric breathe.

The dragon refuses three things and the players should learn them early. It will not kill a surrendered foe. It will not lend its name to a lie (Zone of Truth is on the 1/Day list and it uses it on its own oaths). And it will not stay to fight a battle that isn't the one it agreed to. If the party tries to extend, the dragon politely declines and casts Teleport. Pay this off so the players don't resent the limit later.

Have the dragon ask each PC one direct question before it leaves, and write down the answers. A silver remembers what mortals choose to say to it, and a follow-up two sessions later, where an NPC quotes the answer back, makes the alliance feel real instead of transactional.

An ancient silver dragon as adversary is almost always a misunderstanding played at full volume. Silvers are lawful good and prefer humanoid form, so the encounter usually opens with the dragon standing in for some other figure (a high priest, a queen's advisor, a wise hermit) and only reveals its true shape when the party crosses a line it considers sacred. Sell the social scene first. The fight starts when the party pushes past the warning.

Once it goes Gargantuan, the dragon takes off and opens with Cold Breath. 67 cold damage on a failed DC 24 Con save in a 90-foot cone is a party-wipe shape if everyone clusters. Recharge means it'll be back. Between breaths, Multiattack is three Rends at +17 for 19 slashing plus 9 cold each, and one of those Rends can be swapped for Paralyzing Breath, also DC 24, also a 90-foot cone. First failure is Incapacitated, second is Paralyzed for up to a minute. That's the round you mark the cleric. Spellcasting at-will Hold Monster (DC 23) is the redundant lockdown if breaths aren't recharging. Save the 1/Day Ice Storm for when the party tries to converge.

Legendary actions are the encounter's heartbeat. Cold Gale shoves a 60-foot line up to 30 feet away (DC 23 Dex, 14 cold), which is how you reset position when a paladin sticks to you. Pounce buys a Rend off-turn. Chill spends a legendary to fire Hold Monster again. Spread the three actions across three different player turns, not all on one. Legendary Resistance 4/day (5 in lair) eats the party's biggest control spells. Burn one early on a Banishment so the players know the budget is real, then save the rest for Counterspell-priority moments.

Silvers do not fight to the death over pride. If the party demonstrates good faith mid-combat, or if the dragon realizes it was wrong, it lands, dispels its breath, and asks for parley. Have it leave Zone of Truth running on the floor. The campaign survives the encounter, and the party gains an enemy or an ally for life depending on how they speak in the next two minutes.

Write the dragon's humanoid name on a card before session and use that name for the whole social scene. The reveal lands harder when the players have been calling someone "Lady Aldess" for an hour.