Domain Expansion

Sorcerer (Draconic Bloodline)

Depending on the Draconic Bloodlines option you choose; it might be in a middle of an active volcano with bursting heat and magma that deals fire damage that represents the Red Dragon lineage or a cold winter storm, dealing cold damage at the start of their turn due to your White dragon heritage. In any case use the habitat of the draconic bloodline that you choose to determine the Domain Effects

Wizard (Evocation)

Your spell that you have always prepared might be the determining factor of the domain, or you might use the mightiest spell you could cast as the base of the Domain effects. For example; you have the spell Time Stop prepared, your domain would have clock that has stopped working floating in the middle empty void with a black hole in the distance that has a halo ring as everyone inside of the domain has been moving slower than usual.

Druid (Circle of the Land)

Your domain as a druid might be what you imagine nature looks like if they became alive, trees nearby can awakened becoming a Treant and elemental creature might suddenly appear within the domain, such as an earth elemental. These creatures will consider you as an ally and fend off intruders that you have captured within your domain.

Bard (College of Lore)

You recreate the scenery that you have envisioned in your mind from the epic sagas you have heard and have internalized for you to feel its energy and drama in it. For instance, you have heard and internalized the epic saga of heroes defeating a powerful Elder Lich at the Anauroch desert and emerges triumphant at last, your domain might become a backdrop themed battlefield, full soldiers clad in armor and holding spike as the tidal wave of zombies and skeletons came down to face off against the living from a far distance. 

Sorcerer (Draconic Bloodline)

(Red Dragon) You can cast Scorching ray at 3rd level as a bonus action at each of your turn without expending a spell slot. Each time you use Domain Expansion, you gain a feature to make the ground below any creature to erupt with magma, creature that is within 15 ft. of the eruption must make a dexterity saving throw or take 12d6 fire damage or half on a successful one and knocked prone on a fail save.

Special Action: You can control the magma at will, at the start of your turn you could choose to have the magma lashes to a nearby enemy, dealing 2d12 fire damage.

(White Dragon) You can cast [spell] Rime's binding ice at 3rd level as a bonus action at each of your turn without expending a spell slot. Once per long rest you can conjure spikes of ice from the ground, each creature that is within 15 ft. must succeed on dexterity saving throw or receive 4d6 cold and 4d6 piercing damage and be knocked [condition]prone[/prone]

Special Action: You control the freezing ice within the domain at will, at the start of your turn you can cause an icy cyclone to appear on an area that is 10 ft. in diameter, each creature that is within the area will receive 2d6 cold damage and cannot take any reaction and bonus action.

Wizard (Evocation)

(Time Stop) Your domain warps time and space itself, any creature within the domain must succeed on Charisma saving throw or be affected by the slow spell.

Spell Action: Your mastery over the flow of time is unrivaled in your domain. All creatures within the area is affected by one of the following effects; time ravage, to reroll a saving throw or attack rolls with disadvantage, regain a feature that would normally resets on a short or a long rest, such as action surge and Spellcaster's spell slots, resurrecting dead creatures to life and resets their statistic when they first time enter your domain, and you make a creature frozen in space and unable to make any actions, if they succeed on a constitution saving throw against your magic, they are affected by the slow spell until they exit your domain. You cannot use the same effects on another creature if you already used it on a different creature 

Druid (Circle of the Land)

You conjure several monster to aid you in battling your foe, you can summon Treants, Elementals, Fey and Beasts with challange rating that did not exceed your level, you can summon multiple creature in this manner as long as their combine challange rating is lower or equal to your Druid's level.

Special Action: You can animate the vines and the terrain at will, you transform your domain into a difficult terrain and controlling the vines, rocks and roots to grapple the enemy and lashing or slamming at them dealing 2d6 bludgeoning damage and be knocked prone

Bard (College of Lore)

Your inspiration has lead you to be able to conjure 20 ft. wide sandstorm, obstructing the enemy's views and making it a difficult terrain. You and your ally gain advantage in all saving throw and attack rolls. Additionally, you gain additional inspiration die up to your proficiency bonus and this stacks on top of your regular inspiration die. You can also cast Silvery Barbs as a bonus action without expending a spell slot.

Special action: You can summon a spectral ghost of your heroes saga to attack a creature in your domain, they can cast a spell that you know and learn if its a Spellcaster up to 6th level or they can attack three times with a weapon attack if they are a melee fighter. 

Equal

Your domain cancel each other and the barrier slowly dissolves as they clashed with each other

Over 5

Over 10

You summon your Domain Expansion with its full effects