Eladrin (MToF)
Eladrin are perhaps the most confusing creatures to look up in 5e right now, as befitting their capricious nature.
They are simultaneously an Elf Subrace, a Variant Elf Subrace, a Race of their own, and a Fey Creature. (Most) Eladrin come in a variant for each season of the year, but can change their season with a long rest. Which means that even though these are technically 4 different stat blocks, a long-term NPC ally or enemy could use any of them at any given time. The Book recommends changing the stat block whenever the Eladrin in question is overcome by a particular type of emotion: Goodwill for Autumn. Joy for Spring. Anger for Summer. And Sorrow for Winter. Or you could have them change with the Seasons themselves, or perhaps after being exposed to a particular elemental energy for a bit. There are more than a few options here if you are looking to use them as a Puzzle monster.
All of these Eladrin received a generous boost to their HP, at the cost of their resistance to non-magical weapons. To be fair, any party fighting CR 10 monsters should already have magic weapons, making that resistance mostly fluff.
Autumn Eladrin
The fall comes with a bountiful harvest, and the Autumn Eladrin are all about peace and food. As such, they don't particularly enjoy combat, and though there is a significantly more devastating routine they can use, consider using the following for flavor instead.
In combat, Autumn will try to stop the fight by using its Enchanting Presence and Foster Peace power. For their multiattack option, they cast Hold Person first, hoping to pacify an enemy, and then lay into any enemies that aren’t controlled with their Longsword, hoping to knock the target out with a melee strike. Fey Step is a multipurpose movement tool should there be a need for extra distance in any situation.
The Autumn also has access to a full spread of healing spells, allowing them to counter nearly every kind of status condition that might be thrown at their friends and themselves, including the ability to cast Revivify once per day.
In the Changeover, the Autumn lost a lot of useful spells. Calm Emotions, Heal, and Raise Dead being the biggest losses to their toolkit. In return they received Revivify and a massive DPR boost (that’s kind of weird for a pacifist creature) via Multiattack and increased damage on their basic attacks. They also received resistance to Psychic Damage.
Spring Eladrin
Spring Eladrin are obsessed with joy, and love to beguile creatures to make them joyous as well. That said, they aren’t pacifists like their Autumn kin, so they can actually lay down the beatdown, so long as they humiliate you while doing it.
In combat, the Spring will use its multiattack to cast Tasha’s Hideous Laughter. Which sets a target up to be prone and incapacitated, allowing for advantage on melee attacks against them. They also have access to Major Image to trick enemies should the situation arise.
In the changeover, the Spring gained Psychic resistance, and extra damage for their attacks. In return they lost nearly all of their spells, being left with only Tasha’s Hideous Laughter, Suggestion, and the new addition of Major Image.
Summer Eladrin
Summer Eladin represent Anger and Wrath. Which is ironic considering they are technically weaker than the previous two entries. Maybe.
The standard reading of the monster makes you think they are supposed to be a melee creature. They have a fear aura, a parry reaction, and their most powerful attack is their two-handed longsword strike.
Don’t fall for it.
Instead use their superior mobility and extreme range longbow attacks to assault enemies. They don’t have spells to augment their Multiattack, and there is no reason for them to ever get in close ranged combat considering their attacks are actually weaker than an Autumn Eladrin. Yeah, they have a high STR score, but like, they also have 50’ of movement speed and the ability to teleport away when they get cornered, so why wouldn't they use the superior combat option?
In the Changeover, the Summer received a small amount of extra fire damage on their attacks, and fire resistance.
Winter Eladrin
Winter Eladrin are sorrowful, and make everyone around them feel sad. Fighting a Winter Eladrin is an exercise in overcoming futility.
In combat the Winter will rely heavily on its Sorrowful Presence. Which not only charms enemies, it causes them to have disadvantage on all saving throws and checks. You will note that none of the Winter’s spells cause damage, meaning they are free to let them rip with impunity. A particularly nasty trick would be to push someone off a cliff with Gust of Wind. Though Sleet Storm is probably the best option, not only does it block line of sight to prevent ranged attacks, it causes the area (including the air to thwart flying creatures) to become difficult terrain, and forces a dex save to avoid becoming prone. When someone finally breaks through these layers of defenses, they will find themselves hit by a Frigid Rebuke for their troubles. The Winter does have a multiattack that allows them to cast spells, but the spells should be a top priority. They want to create a situation where they fight one opponent at a time to maximize their chances and action economy, and if that means they block their own line of sight to the rest of the group, then so be it.
In the changeover, the Winter lost all of their damaging spells, but gained Sleet Storm. They also received a moderate damage buff on their weapon attacks.
