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I don’t remember seeing arcanians anywhere else before, though they do have that “late-3e feeling” to them.
Wizardry is a craft that demands great patience and care. While a warlock “cheats” by making shady deals with dubious entities, a wizard earns every bit of power they have. But some wizards have less than great patience and care, and try to reach a bit too far beyond their current ability.
In the vast majority of cases that just results in an embarrassing fizzle, but sometimes the magic goes out of control and causes a major accident. Most of those end up turning the caster into a messy stain on the floor, but some are worse.
In these rare cases, the wizard absorbs most of the runaway magic, which kills them and animates the corpse. The resulting entity is known as an Arcanian. Its sapient and highly intelligent, but utterly consumed by whatever strong emotion the wizard felt as they died, further warped by the nature of the magic that killed them.
Arcanians are Medium Natural Humanoids (Undead). Each is themed around an element and an emotion, though ironically they have no particular resistance against their own theme element. They have a ground speed of 6 and no special senses. They also carry wizardly implements that give them abilities similar to that of a PC wizard.
Their signature ability is Arcane Surge, an encounter power that triggers when they hit an enemy with an implement power (anything but their basic melee attack). It makes that power deal maximum damage.
Green Arcanians are half-melted monstrosities. Acid seeps from their pores, and their footsteps leave seared footprints. Their driven by envy and a hatred of beauty, which they use acid magic to destroy.
Green Arcanians are Level 8 Artillery with 67 HP. All of their attacks deal acid damage. Their basic melee attack is an Acid Touch, and their basic ranged attack an Acid Bolt that also deals a bit of splash damage to enemies adjacent to the target. Less often they can cast a Stream of Acid (recharge 5+) that does heavy damage and inflicts a -2 AC penalty and 5 ongoing acid damage (save ends both).
Their implement power is Orb of Denial, an interrupt which triggers when an enemy succeeds on a save and makes them fail the save instead. Thankfully this is an encounter power.
This shivering corpse despises warmth, and believes that people and things can remain forever perfect if they’re frozen. As you might imagine, it goes around attempting to preserve everything it likes.
Blue Arcanians are Level 10 Controllers with 105 HP. They move slightly slower than normal at Speed 5, and all of their powers deal cold damage.
Their basic melee attack is a Frost Staff that also pushes 2 squares and immobilizes for a turn. They fight at range with at-will Bolts of Frost that turn the area surrounding the target into difficult terrain for a turn, and once per encounter they can summon a Swirling Blizzard to deal damage over an area (half on a miss).
Their implement power is Staff of Shielding, which once per encounter gives them +4 to all defenses against an attack.
These eternally burning undead are gripped in the throes of fiery passion or red-hot wrath. They want to burn the world and take great pleasure in doing so.
Red Arcanians are considerably more powerful than the rest: Level 19 Artillery with 131 HP. All of their attacks deal fire damage, and they carry wands.
Their melee basic attack is a Fiery Touch, and their ranged spells will be familiar to PC wizards: Scorching Burst is an at-will area attack, and Burning Hands is an encounter power that hits a close blast 5 that deals heavy damage and pushes 3 squares.
Their implement encounter power is Wand of Accuracy, which gives them a +4 bonus to their next attack.
Just because liches are the most iconic undead wizards, it doesn’t mean they’re the only ones. Arcanians seem like a good monster to use when you want to make an adventure themed around wizards who dug too deep.
You could have a whole ruined academy filled with a variety of them and with other supporting undead or summoned extra-planar monsters. It’s easy enough to change the ruling element of the stat blocks presented here, or to adjust their level so you can have all three in the same dungeon. Maybe there’s a tome or artifact in its vaults that the party must recover, or maybe it’s just a place they need to pass through on their perilous journey.
Sprinkle in journal entries that hint at the disaster that destroyed the place, and add a big lich with multiple elemental attacks as the “end boss”. And there you have it, an instant Dark Souls level for your 4e table.