Circle of the Primeval

The Circle of the Primeval teaches that, though the land may change over time, it never truly forgets. By tapping into the timeworn memory of the earth, these druids summon and bond with the spirit of a primeval behemoth—a hulking creature that once ruled the ancient world alongside the giants. The most well-known primeval behemoths are the dinosaurs, but spirits bonded with members of the Circle of the Primeval have also taken the form of ancient predecessors to today’s common beasts and other fantastical titanic creatures.

Working alongside their companion spirit, most druids of the Circle of the Primeval spend their lives delving into long-forgotten places and preserving the remnants of bygone eras. As a druid’s power grows, so does their companion, the beast starting near equal in size to its druid partner before increasing in stature until it too towers over the land.

The Circle of the Primeval teaches that, though the land may change over time, it never truly forgets. By tapping into the timeworn memory of the earth, these druids summon and bond with the spirits of primeval behemoths—hulking creatures that once ruled the ancient world alongside the giants.

Keeper of Old

Your connection to the mighty primeval behemoths allows you new insight into the ancient world. You gain proficiency in the History skill. When you make an Intelligence (History) check, you can roll a d4 and add the number rolled to the ability check.

Primeval Companion

Starting when you choose The Circle of the Primeval, you can call upon the primeval creature whose spirit is bound to you. As an action, you can expend one use of your Wild Shape feature to summon your primeval companion, rather than assuming a beast form. The companion appears in an unoccupied space of your choice within 30 feet of you. The primeval companion is friendly to you and your companions, and it obeys your commands.

When you summon your companion, you can determine the cosmetic appearance of the companion; for example, your companion may evoke ancient predators like raptors or saber-toothed tigers, or it might be more inclined for defense, appearing as an armored ankylosaurus or a wooly rhino. Based on your varying companion, you can choose ONE of three abilities: Forceful, Mobile, or Intercept. 
The Companion's PB is equal to your proficiency bonus. Its AC is equal to 13 + PB and HP is equal to 10 plus 5 times your Druid level. It's attacks will scale with PB as well.
In combat, the companion shares your initiative count, but it takes its turn immediately after yours. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take another action. That action can be one in its stat block or some other action. If you are incapacitated, the companion can take any action of its choice, not just Dodge.
The companion remains until it is reduced to 0 hit points or until you die, at which point the companion vanishes. If you use this feature to summon the companion again and you already have a companion present, the first companion immediately vanishes. Anything the companion was wearing or carrying is left behind when the companion vanishes.

Prehistoric Conduit

You learn how to channel your magic through your primeval companion. When you cast a spell with a range other than self, the spell can originate from you or your primeval companion.
In addition, if the primeval companion is affected by a spell you cast that allows creatures to make a saving throw against its effects, the primeval companion has advantage on its saving throw. If the primeval companion would normally take half damage on a successful save against this spell, the companion instead takes no damage on a successful save and half damage with no additional effects on a failed save.

Titanic Bond

At 10th level, your bond with your Primeval Companion has strengthened enough to make its attacks Magical for the purpose of overcoming resistance to non-magical bludgeoning, piercing, or slashing attacks.

Additionally, you have the spell Enlarge/Reduce always prepared. You can cast this spell on your Companion without using a spell slot, but using a wildshape charge. You can also cast the spell normally, using any level spell slot. When casting on your Companion, the Companion maintains concentration rather than yourself.

Scourge of the Ancients

You have learned to fully harness the ancient legacy of your companion. As part of the bonus action you use to command your companion, you can expend a spell slot of any level to heighten your primeval companion’s might, granting it the following benefits:

Behemoth. The companion becomes one size category larger and gains temporary hit points equal to 10 times the level of the spell slot expended. If there isn’t enough room for the companion to become grow to this size, it attains the maximum possible size in the space available.

Mauler. On a hit, the companion’s Strike deals additional damage equal to 1d8 plus the level of the spell slot expended.

Titanic Stride. The companion’s walking speed increases by a number of feet equal to 5 times the level of the spell slot expended.

These benefits last for 1 hour, until the companion vanishes, or until you expend a spell slot for this feature again.