Serra, the Sculptor

Legendary Planeswalker - Serra

Whenever an angel you control enters, put an amount of loyalty counters on Serra equal to its toughness.

+1 Create a 4/4 white angel creature token with flying and vigilance.

-4 Exile target creature. Its controller gains life equal to its power.

-20: Exile all nonland permanents you don't control.

3

Create a snow elemental.

Benjen, Beamtown Juggernaut

Legendary Planeswalker - Benjen

Rhinos you control get +2/+2 and gain vigilance and trample.

+1 Destroy target noncreature permanent. Its controller creates a 3/3 green rhino creature token.

-3 Reveal cards from the top of your library until you reveal a rhino creature card. Put that card onto the battlefield, then shuffle the rest into your library. When a creature enters this way, it gains "When this creature enters, it fights up to one target creature you don't control."

5

Benjen, Beamtown Juggernaut can be your commander.

Create a mythic rare sloth creature.

Crow_Umbra: Ah crap, I meant to write nontoken artifact, so you couldn't just blow up your own food tokens for lands.

Timbles, Obsessive Nibbler

Legendary Creature - Beaver Berserker

Islandwalk

Whenever this creature enters or attacks, destroy target nonartifact artifact or enchantment. Its controller may search their library for a basic land card, put it onto the battlefield tapped, then shuffles.

On Bloomburrow, Timbles wrecked some havoc. On Kamigawa, he could hardly not wreck all of it.

3/4

Repeat.

Duskwalker Sentinel

Artifact Creature - Gargoyle

Flying, Defender

Whenever this creature or another gargoyle you control enters, gargoyle creatures you control may attack as though they didn't have have defender.

4/5

This sat quite a while. If you want to, continue with simic. Otherwise, just do wild.

You might be interested in Tarrian's Soulcleaver. You mentioned giving Mag vigilance before wiping during an attack. Cleaver is the perfect weapon for that.

Song of Increasing Foresight

Enchantment - Saga

Scry X, where X is the number of lore counters on this saga.

: Until end of turn, you may cast a spell with mana value X from your hand without paying its mana cost, where X is the number of lore counters on this saga.

This seems pretty printable to me.

Create a cat warlock.

Death-Knell Shinobi

Creature - Human Ninja

Whenever this creature enters or attacks, you may tap an untapped artifact you control. If you do, destroy target creature if its mana value is equal to that artifact's mana value.

Ninjutsu

3/3

In an average room, there are 37 objects she can drop on you before you even notice.

Create a angel.

We've had the Ungali pretty recently, as another fraction from the blind eternities. But I have another idea:

Uuur, Plowbeast Ultimus

Legendary Creature - Ox Aurochs

Mutate

Trample, Annihilator 1

Whenever this creature or another Oxen or Aurochs you control mutates, exile target creature. It's controller searches their library for up to one basic land card, puts it onto the battlefield, then shuffles.

5/5

Wild.

Klorsh, Titan of Twilight's Pull

Legendary Creature - Elder Giant

When this creature enters, sacrifice it unless it escaped.

Whenever this creature enters or attack, target player discards two cards. You gain 4 life for each nonland card discarded this way, then you draw a card for each land card discarded this way.

Escape , exile five other cards from your graveyard.

6/6

Create a legendary MV6 Knight in Mardu colors.

Kelad: Even though I already dismantled the deck a while ago, this is great advice! Thank you very much, this might be exactly what the deck needed. I'm not sure if I'll rebuild it, but at least I'll absolutely consider your advice if I do so.

Gutburst Wurm

Creature - Wurm

Ward - Sacrifice three creatures.

Whenever another creature dies, exile it from its owner's graveyard.

At the beginning of your end step, if 10 or more cards are exiled with ~, sacrifice it, then return each creature card exiled this way to the battlefield under your control. If at least 30 cards are exiled with ~, you win the game instead.

7/7

Its hunger knows no boundary except the walls of its abdomen.

So Esper is left.

Area Annihilator

Creature - Ungali

When this creature you control enters, sacrifice five non-Ungali permanents you control.

Creatures attacking you have Annhiliator 1.

: Put this creature card from your hand onto the battlefield under target opponent's control.

8/8

To differentiate Ungali from Eldrazi, why not give them a way to enter the opponent's board, causing massive havoc over there? So let's see another Ungali.

Haphaestol, God of the Anvil

Legendary Enchantment Creature - God

Indestructible

As long as your devotion to white, blue and red is less than 10, ~ isn't a creature.

Whenever an equipment you control enters, you may create a 1/1 white, blue and red demigod creature token and attach that equipment to it.

: Attach any number of equipments you control to target creature.

4/6

Create a legendary WUBRG wurm.