Do you want to build a snowman?
I was going to make a suggestion for a Snow Minion Mastermind powerset since it's such low hanging fruit. The assets already exist, and it seems like it would be easy to implement and balance overall. It also definitely fits some power tropes. My issue with the suggestions above is when everything is a priority, then nothing is a priority, so this idea just got mixed into the wash above. Looking at the individual post from 2019, the Ice Elemental design looks mostly solid, but there were some issues with it, so I'm making some tweaks to the original design. The original suggestion was:
Ice Elementals: Through various means you can call forth the powers of winter to serve you and destroy your foes. Ice elementals are exceedingly resilient and slow down their foes substantially but are vulnerable to fire damage and somewhat slow. Special ability: Brittle cold, struck by multiple elementals (including the mastermind) gain a "brittle" proc that can allow 1.5x critical hits to be dealt to them with each proc of "brittle" increasing the chance of this by 5%.
T1: Ice Bolt (as per Ice Blast)
T2: Frostlings (Basically the winter horde enemy. Equip adds Ice Armor. Enhance adds Block of Ice.)
T3: Ice Blast (as per well...Ice Blast)
T4: Empower Cold (Equip power)
T5: Freeze Ray
T6: Summon Jack Frosts (Starts with Freezing Touch and Ice Sword. Equip adds Glacial Shield and Breath of Frost. Enhance adds Wet Ice and Ice Patch
T7: Stay Frosty (Targeted AoE with hold and minor DoT over time; every held enemy defeated while held has a chance to spawn a frostling)
T8: Summon Hellfrost: (Starts with Ice Sword and Greater Ice Sword. Equip adds Energy Absorbtion, Wet Ice, and frostwork. Enhance adds Freezing Aura and Hibernate.)
T9: Permafrosting (Enhance power)
I propose a number of modifications to the suggestion both to simplify and use assets so coding is minimal. First, I don't think other mastermind sets have special powers most of the time, so remove the brittle suggestion. I understand that animals have a power, but they are exclusively melee. This set has some ranged options. Second, I'd stick to the existing assets for the Winter Horde in order to make assets super easy to adopt. The idea here is to give new balanced options without having to do a bunch of development...low hanging fruit.
T1: Ice Bolt - Ice Bolt quickly pelts an enemy with small icy daggers
From Ice Blast powerset (T1)
T2: Summon Frostlings - Calls forth one to three frostlings (depending on your level) to do your bidding
Winter Horde Enemy has Ice Bolt, Frost, Resistance. Don't see a reason to change this.
Equip adds Frozen Armor from Ice Armor Set (T1). (Visual Change - Add cryo aura)
Enhance adds Block of Ice from Ice Control (T2). (Visual Change - Add change cryo aura from white to light blue)
T3: Ice Blast - Ice Blast hurls shards of ice at foes and Slows their attacks and movement for a time
From Ice Blast powerset (T2)
T4: Fortify - Fortify your snow minions to make them more durable.
Equip power - gives defensive powers to all snow minions
Adds Frozen Armor (T1) to Frostlings
Adds Frozen Armor (T1) and Hoarfrost (T2) to Blights
Adds Frozen Armor, Hoarfrost, and Chilling Embrace to Snow Beast
T5: Freeze Ray - Freeze Ray encases your foe in a block of ice, holding them helpless in place for a while.
From Ice Blast powerset (T5)
T6: Summon Blight - Calls forth one to two Blights (depending on your level) to do your bidding.
Winter Horde Enemy has Chillbain, Ice Bolt, Ice Blast, Frozen Fists, Resistance
Equip adds Frozen Armor and Hoarfrost both from the Ice Armor Set (T1,T2). (Visual Change - Add cryo aura)
Enhance adds Block of Ice from Ice Control (T2) and Frost Breath from Ice Blast (T3). (Visual Change - Add change cryo aura from white to light blue)
T7: Permafrost
As Frostwork (Cold Domination T5) but casts on all minions permanently
T8: Summon Snow Beast - Calls one massive Snow Beast.
Winter Horde Enemy has Ice Blast, Freeze Ray, Frost Breath, Frozen Fists, Winter Storm, Resistance
Equip adds Frozen Armor, Hoarfrost, and Chilling Embrace, all from the Ice Armor Set (T1, T2, T3). (Visual Change - Add cryo aura)
Enhance adds Block of Ice from Ice Control (T2), Build Up from Ice Blast (T4), Snow Storm (Cold Domination T3) (Visual Change - Add change cryo aura from white to light blue)
T9: Rein of Winter - Upgrades snow minions making them more capable offensively
Enhance power, giving offensive options
Adds Block of Ice to Frostlings
Adds Block of Ice and Frost Breath to Blights
Adds Block of Ice, Build Up, and Snow Storm to Frost Beast
This should be easy to balance, uses almost exclusively existing assets. Shouldn't cause power creep.