Overwhelming Encounter

Creatures you control gain vigilance and trample until end of turn. Roll a d20.
1—9 | Creatures you control get +2/+2 until end of turn.
10—19 | Put two +1/+1 counters on each creature you control.
20 | Put four +1/+1 counters on each creature you control.

Wyll, Blade of Frontiers

If you would roll one or more dice, instead roll that many dice plus one and ignore the lowest roll.
Whenever you roll one or more dice, put a +1/+1 counter on Wyll, Blade of Frontiers.
Choose a Background (You can have a Background as a second commander.)

Chaos Channeler

Wild Magic Surge — Whenever Chaos Channeler attacks, roll a d20.
1—9 | Exile the top card of your library. You may play it this turn.
10—19 | Exile the top two cards of your library. You may play them this turn.
20 | Exile the top three cards of your library. You may play them this turn.

Thunderwave

Roll a d20.
1—9 | Thunderwave deals 3 damage to each creature.
10—19 | You may choose a creature. Thunderwave deals 3 damage to each creature not chosen this way.
20 | Thunderwave deals 6 damage to each creature your opponents control.

Brazen Dwarf

Whenever you roll one or more dice, Brazen Dwarf deals 1 damage to each opponent.

Iron Mastiff

Whenever Iron Mastiff attacks, roll a d20 for each player being attacked and ignore all but the highest roll.
1—9 | Iron Mastiff deals damage equal to its power to you.
10—19 | Iron Mastiff deals damage equal to its power to defending player.
20 | Iron Mastiff deals damage equal to its power to each opponent.

The Space Family Goblinson

The Space Family Goblinson has trample as long as you've rolled three or more dice this turn.
Whenever you roll a die, put a +1/+1 counter on The Space Family Goblinson.

Vrondiss, Rage of Ancients

Enrage — Whenever Vrondiss, Rage of Ancients is dealt damage, you may create a 5/4 red and green Dragon Spirit creature token with "When this creature deals damage, sacrifice it."
Whenever you roll one or more dice, you may have Vrondiss deal 1 damage to itself.

Journey to the Lost City

At the beginning of your upkeep, exile the top four cards of your library, then roll a d20.
1—9 | You may put a land card from among those cards onto the battlefield.
10—19 | Create a 2/2 green Wolf creature token, then put a +1/+1 counter on it for each creature card among those cards.
20 | Put all permanent cards exiled with Journey to the Lost City onto the battlefield, then sacrifice it.

Centaur of Attention

When Centaur of Attention enters the battlefield, roll five six-sided dice and store those results on it.
At the beginning of combat on your turn, you may reroll any number of Centaur of Attention's stored results.
Centaur of Attention gets +X/+X, where X is the greatest number of stored results on it of the same value.

Raised by Giants

Commander creatures you own have base power and toughness 10/10 and are Giants in addition to their other types.

Sword of Hours

Whenever equipped creature attacks, put a +1/+1 counter on it.
Whenever equipped creature deals combat damage, roll a d12. If the result is greater than the damage dealt or the result is 12, double the number of +1/+1 counters on that creature.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Neverwinter Hydra

As Neverwinter Hydra enters the battlefield, roll X d6. It enters with a number of +1/+1 counters on it equal to the total of those results.
Trample
Ward {4} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {4}.)

Wyll's Reversal

Choose target spell or ability with one or more targets. Roll a d20 and add the greatest power among creatures you control.
1—14 | You may choose new targets for that spell or ability.
15+ | You may choose new targets for that spell or ability. Then copy it. You may choose new targets for the copy.

Critical Hit

Target creature gains double strike until end of turn.
When you roll a natural 20, return Critical Hit from your graveyard to your hand. (A natural 20 is a roll that displays 20 on the die.)

Farideh's Fireball

Farideh's Fireball deals 5 damage to target creature or planeswalker. Roll a d20.
1—9 | Farideh's Fireball deals 2 damage to each player.
10—20 | Farideh's Fireball deals 2 damage to each opponent.

Chaos Dragon

Flying, haste
Chaos Dragon attacks each combat if able.
At the beginning of combat on your turn, each player rolls a d20. If one or more opponents had the highest result, Chaos Dragon can't attack those players or planeswalkers they control this combat.

Wand of Wonder

{4}, {T}: Roll a d20. Each opponent exiles cards from the top of their library until they exile an instant or sorcery card, then shuffles the rest into their library. You may cast up to X instant and/or sorcery spells from among cards exiled this way without paying their mana costs.
1—9 | X is one.
10—19 | X is two.
20 | X is three.

Song of Inspiration

Choose up to two target permanent cards in your graveyard. Roll a d20 and add the total mana value of those cards.
1—14 | Return those cards to your hand.
15+ | Return those cards to your hand. You gain life equal to their total mana value.

Vegetation Abomination

Deathtouch
{T}, Sacrifice Vegetation Abomination: Roll a six-sided die. You gain life equal to the result.

Vexing Puzzlebox

Whenever you roll one or more dice, put a number of charge counters on Vexing Puzzlebox equal to the result.
{T}: Add one mana of any color. Roll a d20.
{T}, Remove 100 charge counters from Vexing Puzzlebox: Search your library for an artifact card, put that card onto the battlefield, then shuffle.

Clay Golem

{6}, Roll a d8: Monstrosity X, where X is the result. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)
Berserk — When Clay Golem becomes monstrous, destroy target permanent.

Druid of the Emerald Grove

When Druid of the Emerald Grove enters the battlefield, search your library for up to two basic land cards and reveal them, then roll a d20.
9 or less | Put those cards into your hand, then shuffle.
10—19 | Put one of those cards onto the battlefield tapped and the other into your hand, then shuffle.
20+ | Put those cards onto the battlefield tapped, then shuffle.

Ancient Bronze Dragon

Flying
Whenever Ancient Bronze Dragon deals combat damage to a player, roll a d20. When you do, put X +1/+1 counters on each of up to two target creatures, where X is the result.

Goblin Anarchomancer

Each spell you cast that's red or green costs {1} less to cast.

Berserker's Frenzy

Cast this spell only before combat or during combat before blockers are declared.
Roll two d20 and ignore the lower roll.
1—14 | Choose any number of creatures. They block this turn if able.
15—20 | You choose which creatures block this turn and how those creatures block.

Sakura-Tribe Elder

Sacrifice Sakura-Tribe Elder: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Calamity Bearer

If a Giant source you control would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Barbarian Class

(Gain the next level as a sorcery to add its ability.)
If you would roll one or more dice, instead roll that many dice plus one and ignore the lowest roll.
{1}{R}: Level 2
Whenever you roll one or more dice, target creature you control gets +2/+0 and gains menace until end of turn.
{2}{R}: Level 3
Creatures you control have haste.

Component Pouch

{T}, Remove a component counter from Component Pouch: Add two mana of different colors.
{T}: Roll a d20.
1—9 | Put a component counter on Component Pouch.
10—20 | Put two component counters on Component Pouch.

The Deck of Many Things

{2}, {T}: Roll a d20 and subtract the number of cards in your hand. If the result is 0 or less, discard your hand.
1—9 | Return a card at random from your graveyard to your hand.
10—19 | Draw two cards.
20 | Put a creature card from any graveyard onto the battlefield under your control. When that creature dies, its owner loses the game.

Pair o' Dice Lost

Roll two six-sided dice. Return any number of cards with total mana value X or less from your graveyard to your hand, where X is the total of those results. Exile Pair o' Dice Lost.

Bag of Tricks

{4}{G}, {T}: Roll a d8. Reveal cards from the top of your library until you reveal a creature card with mana value equal to the result. Put that card onto the battlefield and the rest on the bottom of your library in a random order.

Sylvan Shepherd

Vigilance
Whenever Sylvan Shepherd attacks, roll a d20.
1—9 | You gain 1 life.
10—19 | You gain 2 life.
20 | You gain 5 life.

Earth-Cult Elemental

Siege Monster — When Earth-Cult Elemental enters the battlefield, roll a d20.
1—9 | Each player sacrifices a permanent.
10—19 | Each opponent sacrifices a permanent.
20 | Each opponent sacrifices two permanents.

Atomwheel Acrobats

Whenever you roll a 1 or 2, put that many +1/+1 counters on Atomwheel Acrobats.
{2}{G}: Roll a six-sided die.

Delina, Wild Mage

Whenever Delina, Wild Mage attacks, choose target creature you control, then roll a d20.
1—14 | Create a tapped and attacking token that's a copy of that creature, except it's not legendary and it has "At end of combat, exile this creature."
15—20 | Create one of those tokens. You may roll again.

Hoarding Ogre

Whenever Hoarding Ogre attacks, roll a d20.
1—9 | Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
10—19 | Create two Treasure tokens.
20 | Create three Treasure tokens.