My attempt at making an Alternate or Revised Beast Master subclass for Ranger.

Beast Master Ranger's have a unique connection with nature and the creatures who occupy it. They form deep bonds and friendships with beasts and work together to protect against those that would threaten to destroy the realm. 

Ranger’s Companion

At 3rd level, you gain a beast companion that accompanies you on your adventures and is trained to fight alongside you. Choose a beast of challenge rating 1/2 or lower that is of medium size or smaller. Once bonded, the beast can speak, read, and write Druidic and its Intelligence score changes to 8. It also gains darkvision out to a range of 60 feet if it doesn't already. It's AC is equal to the one outlined in its stat block + your proficiency bonus and it adds your proficiency bonus to any of it's attack rolls. The companion has a number of hit die equal to your Ranger level. It's hit die is determined by the one used in it's original stat block. For example, a Wolf companion would have d8 hit dice and, if you are level 3, it would have 3d8 + 3 (16) hit points. Your companion retains all of its ability scores except for it's Intelligence score and also retains any skill proficiencies and senses outlined in it's original stat block, including abilities, actions, bonus actions, etc. It also gains proficiency in either Dexterity or Strength saving throws (your choice) if it doesn't already have one. Finally, your companion gains an additional skill proficiency when you reach the following levels: 7th level, 11th level, and 15th level. The skills are chosen from the following: Perception, Survival, Athletics, Acrobatics, Intimidation,  or Stealth.

Your companion shares your initiative count and takes its turn immediately after yours. It moves and uses 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, your companion can take any action of its choice, not just the Dodge action.

Upon being reduced to 0 hit points, your companion makes death saving throws. Should your companion die, you can bring it back by touching it and expending a spell slot of 1st level or higher so long as it died within 10 minutes. If it has been dead for more than 10 minutes, you must use a diamond worth at least 150 gp and spend 8 hours performing a resurrection ritual. Should the body be destroyed, you can spend 8 hours connecting with a non-hostile beast that fulfills the outlined requirements and gain another companion who would then gain the benefits outlined in your class features.

Magical Bond

At 3rd level, you learn to speak, read, and write Druidic as well as gain proficiency in Animal Handling checks if you don't already. Additionally, gain the ability to telepathically communicate with your companion. The telepathy has a range of 30 feet. At 11th level, this range extends to 60 feet.

You can also cast Beast Sense a number of times equal to your proficiency bonus targeting only your companion, regaining all expended uses upon finishing a long rest.

Path of Growth

As you and your companion go on adventures and grow stronger together, your companion will gain additional benefits and abilities as a result. These will be outlined as you level up and unlock your Beast Companion class features. These benefits take the form of Senses, Additional Movement, Natural Weapons, and Special Traits. They are available as follows: 

Senses 
Your companion can acquire one of the following:
30 ft. Tremorsense
30ft.  Blindsight.

Additional Movement
Your companion can acquire one of the following:
10 ft. increase to their walk speed.
A climb speed equal to their walk speed.
A fly speed equal to their walk speed. (winged or tiny beasts only)
A swim speed equal to their walk speed.
10 ft. burrow speed.

Natural Weapons 
Your companion can acquire one of the following so long as it has the appropriate appendage: 
Bite - Melee weapon attack, reach 5 ft, one target. Hit: 1d8 + their Dexterity modifier piercing damage. 
Claw - Melee weapon attack, reach 5 ft, one target. Hit: 1d6 + their Dexterity modifier slashing damage. 
Gore  - ( medium sized, horned beasts only) - Melee weapon attack, reach 5 ft, one target. Hit: 2d6 + their Strength modifier piercing damage.
Tail - (medium sized, tailed beasts only) - Melee weapon attack, reach 5 ft, one target. Hit: 1d10 + their Strength modifier bludgeoning damage.

If your companion has appendages that aren't listed here, work with your DM to come up with a natural weapon that suits them if none of these would fit.

Special Traits
Second Wind - Once per short rest, as a bonus action, your companion can draw energy from your natural bond, healing itself. It regains 1 of it's hit dice + your ranger level hit points. 
Unbreakable Spirit - Once per long rest, when your companion would take damage that would reduce it's hit points to 0, as a reaction, it can immediately take it's turn. Your companion remains at 0 hit points for the duration of the turn and take death saves if they take damage. At the end of the turn, it succumbs to its wounds and falls unconscious or dead, depending on death saves. 
Durable Hide  - Once per short rest, when your companion takes damage, as a reaction, it can give itself resistance to all of that damage's turn until the start of it's next turn.

Exceptional Training

Beginning at 7th level, your companion and the bond you share has grown stronger. Your companion's attacks now count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage. Additionally, it gains one of the following features: 

Multiattack. Your companion can now make 2 attacks when it takes the attack action and gains a Natural Weapon as outlined in the Path of Growth Feature.

Honed Senses. Your companion's darkvision extends out to 120 feet and it gains an additional Sense as outlined in the Path of Growth feature.

Fleet of Foot. Your companion acquires an Additional Movement as outlined in the Path of Growth feature.

You can unlock another one of these features at 11th level, and 15th level.

Bestial Growth

Starting at 11th level, your companion has approached its peak. Your companion gains the following benefits: 

Enhanced Physique. Your companion grows 1 size larger and it's attacks now deal one additional die of damage. 

Improved Arsenal. Your companion gains a Special Trait as outlined in the Path of Growth feature.

Expertise. Choose 2 of your companion's skill proficiencies. Their proficiency bonus is doubled for any ability check they make with either of the chosen skills. 

Unbreakable Bond

Beginning at 15th level, the bond between you and your companion is unbreakable, and your strength together has reached its pinnacle. When you cast a spell targeting yourself, it can also affect your companion assuming it is within 30 feet of you. Also, when you cast spells such as Hunter's Mark, your companion also gains the benefit of extra damage. 

Additionally, you can tighten your bond and transfer power from your companion to yourself. As an action, you can choose to gain one of your companions senses, skill proficiencies, or special movement types. This benefit lasts for one hour. You can do this a number of times equal to your Wisdom modifier, regaining all expended charges upon taking a long rest. You can expend another charge of this ability to extend it's duration (1 hour for every charge expended) or to choose a different option.