Keen Smell. The tiger has advantage on Wisdom (Perception) checks that rely on smell.

Pounce. If the tiger moves at least 20 feet straight toward a creature and then hits it with a claw attack on the same turn, that target must succeed on a DC 16 Strength saving throw or be knocked prone. If the target is prone, the tiger can make one bite attack against it as a bonus action.

Martial Role. 1st-level Warrior feature.
Defender. See Reactions.

Improved Critical.  3rd-level Warrior feature
The sidekick’s attack rolls score a critical hit on a roll of 19 or 20 on the d20.

Ability Score Improvement. 4th-level Warrior feature (+3 STR, +1 INT, +2 CHA, +4 CON)
At 4th level and again at 8th, 12th, 14th, and 16th levels (so far), the sidekick increases one ability score of your choice by 2, or the sidekick increases two ability scores of your choice by 1. The sidekick can’t increase an ability score above 20 using this feature.

Battle Readiness. 7th-level Warrior feature
The sidekick has advantage on initiative rolls.

Improved Defense.10th-level Warrior feature
The sidekick’s Armor Class increases by 1.

Indomitable.11th-level Warrior feature
The sidekick can reroll a saving throw that it fails, but it must use the new roll. When it uses this feature, it can’t use the feature again until it finishes a long rest. This increased to two uses per long rest at level 18.

Spiked Barding.
When you use the Attack action to grapple a creature, or if you are the victim of a grapple attack, the other party takes (1d4 - 1) piercing damage if the grapple check succeeds.

Extra Attack.
The sidekick can attack three times (1 bite & 2 claws), instead of once, whenever it takes the attack action on its turn.

Bite. Melee Weapon Attack: +11 to hit (Crit on 19-20), reach 5 ft., one target. Hit: 10 (1d10 + 5) piercing damage.

Claw. Melee Weapon Attack: +11 to hit(Crit on 19-20), reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage.

Second Wind. (2nd level Warrior feature) 
The sidekick regains hit points equal to 1d10 + its level (here, CR).  Once it uses this feature, it must finish a short or long rest before it can use it again.

Defender. The sidekick can use its reaction to impose disadvantage on the attack roll of a creature within 5 feet of it whose target isn’t the sidekick, provided the sidekick can see the attacker.