... in the Future.n

Giants:  Frost Giant, Stone Giant, Hill Giant,...
Elementals: Air Elemental,... Minor Elementals Level 2 for Academy maybe?
More Insect: Ants, a Mantis, Mosquitos.... more Spiders
A Legendary Gigantic Turtel for the Siren
A Shapeshifter with resiland, who adapts the attacks and traits of creatures in his zone.
Oger: Example War Oger, Chainfighter Attacks with range and unavoidable.

A Big Worm in the style as in the Movies "Tremors, Land of Rocket Worms" and "Dune, The Desert Planet"
Example:  Desert Worm Characteristics Slow, Tough -2, Burrow
As long as this creature has a buried marker, it loses the Slow Trait and gets Fast.

New Keyword Burrow: This creature can use a full action to bury itself, Put a Buried marker on this creature. Buried creatures can only be attacked by other Buried creatures in the same zone, attack, spells and skills of other objects in the arena do not affect this creature, As long as it is buried. As soon as this creature attacks an obiekt that does not have a Buried marker , remove the Buried marker from it.

we have the Equipment Wind Wyvern Hide and Storm Drake Hide. I would like to see these creatures if they are not all exterminated.

There are a lot more ...
What would you like to see?

Shadow Assassin
Skaven/Ratman or Dark Elf
120 spellbook points 31 Life 9 Mana
Training:
Traind in War lvl 1 and Dark School (except Demons, and Undead Creatures). Holy school costs the triple.

Characteristics:

Hide in the Shadows
You can use a full action to hide yourself. Pay 2 Mana put an invisible marker on your mage, you are invis until the next Supplyphase or until you use an action. You can only use Hide if there is no enemy creature in your zone.
Sneaky blow from behind
You get +2 Attack Dice Against inactive creatures.

Elusive
The Shadow Assassin has the characteristic Elusive

Basic Meele Attack 3 Damage Dice

https://www.boardgamegeek.com/thread/1698407/thoughts-next-expansion

"Aaron Brosman       Posted Sat Dec 31, 2016

I'm almost 100% positive the next expansion will have Frost damage spells in it. It's something we originally meant to have back in Druid vs. Necromancer, but it ended up not fitting with the Mage we were making. However, unless something pretty drastic happens I'd expect Freeze/Frost Damage to be in the next set. "

When I think of a Frost Mage, Frostwitch comes to me mind.
I Think that"frost"is in the Waterschool at Home, so the Sirene can also use. For the Frost Mage, frost spells will simply be easier to cast or make more damage through equipment, Rings and so on.
But maybe Frost is in Nature School?
Baerskin a lvl 1 Armor 2 Armor Frost -2
Dragonscale Hauberk, Wind Wyvern Hide, Storm Drake Hide,...
What you think about Frost...

Resurgence/Wiederaufleben

If this Creature is on your Discart Pile, you can spend X Mana+1 to get a D12 Dice roll with a result of 7+, this creature returns Inactive to the game, X is the level of the creature.

Example
12 Mana Phoenix, from the Ashes Level 3 Fire, Bird
0 Armor 8 Life
Fast 3 Dice Fire Damage D12 5-9 1Burn, 10+ 2Burn
Hydro +2, Flame Immunity, Flying, Resurgence

 (8 ) Anthill 1 Nature & 1 Earth
Conjuration, Ant   Life 9
Lightnig imunity, fire imunity, Hydro +2
Ant creatures in Anthills Zone get Obscured and ...?...  traids

(16) Ant Qween Level 4 Nature
 Ant, Insect 3Armor 15Life
4 Damage D12 6-9 1Corrode
                      10-12 2 Corrode
-2 Acid, Familier, Unique
Ant Qween can cast only lvl 1-3 Ant spells.


(11) Ant Warrier Level 3  Nature
Ant, Insect 2 Armor 11Life

4 Damage D12 6-9 1Corrode
                    10-12 2Corrode
-2 Acid

(9) Ant Worker Level 2 Nature Ant, Insect
 2Armor 6Life

3 Damage D12 7+ 1 Corrode
-2 Acid

Fast Action Remove 2 Damage from a Corporeal Conjuration in its Zone.
Use a full Action to place 1 mana on Ant Qween

... i want a Beholder for mage wars!

Arkan/Air or Mind  ,maybe as Familier

I talk about RazorTUSK and Timber Wolf!
I think he is something missing (for Academy he is a good Card)

I can understand why the rules have been simplified for Academy,  but disagree about... characteristics that make up a creature, should be included on the card.
Since I play MW  Games, I thought always that the characteristics for the cards are well chosen. In Academy the poor Razor Tusk has its fate not deserved, if he would have Charge +1 he would also playable in the Arena.
Even though Charge is no constituent of Academy it is an constituent of a pig that having Tusks.
... into westeros (Game of Thrones would Robert Baratheon, still sitting on the Throne of the Seven Kingdoms, if it does not, a boar, would have torn his tusks into Roberts stomach.:-)
It would have, Charge, and the other keywords  listet into rulebook of Academy in a separate part, "with the notation "is used" in MW Arena "
The Academy is too small, the boar he can not have enough thrust take for Charge:-)

I think if someone likes MW Academy, he will sooner or later want to try his luck in to the Arena. He will encounter in the Basic Box the Timber Wolf and the poor Pig never see the Sunlight again.

And we MW Arena Player, buy even 1 or 2 boxes of Academy and get a poor pig, this by Charge +1 in would be played in the arena and alternative for timber wolf.

another point we play the arena for a long time a property fact is not / not yet used cold resistens ...
A Cub should have -1 cold, mother bear and her man should be treated equally fact it is almost Discrimination,
that they must freeze.

 For beginners it may be good but he will not Remain a beginner and then he will realize the first very esteemed friend Basically is just a toothless loser.

That with the lightning Raptor is ok not use all birds fly and the Faerie is as small it does not come high enough but flying does she ....