You use your knowledge of animals and how to tame them to have one follow you around and listen to you. The animal is based on the habitat you are in. Though it isn't permanent it allows you to have some utility and more combat effectiveness.

Beast Comapnion

Beginning at 3rd Level you can spend 8 hours and 25 gp to bond with a beast to make it your companion. You make a number of Animal Handling Ability Checks to see if you can tame the beast. The number is based on what Creature Rating it is. In order to tame a beast, you must have more successes than failures. If you fail taming the creature you lose the gold spent and the creature will attack you. If the creature is close to dying it will retreat, Unless the animal’s nature says otherwise.

Creature Rating	Checks Needed	Check(s) DC
0	1	5
1/8	1	10
1/4	1	15

 

You can try to tame a beast that is already under someone else's control, unless by magical means. Depending on the CR the DC and number of checks changes.

Creature Rating	Checks Needed	Check(s) DC
0	1	15
1/8	1	20
1/4	1	25

 

If your beast companion strays too far from its natural habitat, It leaves your service. For example, if a wolf is native to an island, it would be by your side until you leave that island. If the creature leaves, you would have to spend another 8 hours and 25 gp to tame another beast to your side that is native to the current habitat you are in. Repeating the same process as before.

 

Each Beast has a personality and a flaw. Your DM may choose what personality or flaw the beast may have or roll on it on a table.

Roll 1d6	Personality Trait	Roll 1d6	Flaw
1	My idea of a hello is a flurry of licks to the face.	1	I distrust everyone except my master.
2	I have to be next to master unless they tell me otherwise.	2	If a stranger gets too close before I accept them, I bite.
3	I constantly clean myself.	3	I’m only with my master for survival.
4	I sleep next to my master every night.	4	I’ll bite my master if I feel like he disrespected me.
5	I like other animals unless they attack my master.	5	I get distracted by jingling items.
6	I like meeting new people.	6	I don't like being pet.

 

If the beast gets the frightened condition or the confused condition, you can spend an action to cure the beast of the condition by making an Animal Handling check (DC of 10). On a failure, you can’t attempt to cure the condition this way.

The beast uses your proficiency bonus to add to it’s Attack Rolls, Damage Rolls, Skills, and Armor Class. The beast acts on your turn, separately from you. It can't use its multi attack if it has one. If the beast dies, you would have to tame another beast, repeating the process listed above. The beast’s HP is either is base HP or 5 times your Fighter level, whichever is higher.

 

Tamer's Aptitude

Beginning at 3rd level, you gain proficiency in Animal Handling. If you are already Proficient in Animal Handling than you can add double your proficiency bonus to Animal Handling Checks.

Tamer's Bond 1

The Tamer and their Beast companion bond even further, increasing their effectiveness. At levels 7, 10, 15, 18 you features.

Beginning at 7th level, you get Adv. on ability checks that your beast is proficient in. For example, if the beast is proficient with Perception checks. You now have advantage on Perception Checks.

Your beast now can use the Extra-Attack feature, allowing to make up to two attacks if it uses the Attack action on its turn.

Tamer's Bond 2

The Tamer and their Beast companion bond even further, increasing their effectiveness. 

Beginning at 10th level, when ever you use your Second Wind your beast heals the amount of HP that you received. Your beast can also now use the Dash, Disengage, or Help actions as a bonus action.

Tamer's Bond 3

The Tamer and their Beast companion bond even further, increasing their effectiveness.

 

Beginning at 15th level, if your beast is within 30 ft. of its master it can add 1d10 to one damage roll it makes against another creature. Can only be used once a round.

 

Tamer's Bond 4

The Tamer and their Beast companion bond even further, increasing their effectiveness. 

 

Beginning at 17th level, your beast now has access to its own action surge. It regains its use after a short or long rest.