Fire Absorption. Whenever the young adult strider is subjected to fire damage, it takes no damage and regains a number of hit points equal to half the fire damage dealt.

A trusty mount: You are now able to mount this creature.

Armored monstrosity: You are now able to put simple armor on the young adult strider for defensive purposes.

Multi-attack: You can make one bite attack and one fire burst attack.

Bite: Action Melee Attack. Melee Weapon Attack: +5 to hit, reach 10ft., one target. Hit: 7 (2d6 + 3) [piercing] damage.

Tail: Action Melee Attack. Melee Weapon Attack: +5 to hit, reach 25ft, two targets. Hit: 3 (1d4+3)[bludgeoning] damage. 

Fire Burst (Recharge 5-6) Action Ranged Attack. Ranged Weapon Attack: The young adult strider hurls a gout of flame at a point it can see within 60 feet of it. Each creature in a 20-foot-radius sphere centered on that point must make a DC 12 Dexterity saving throw, taking 5 (1d8+3) fire damage on a failed save, or half as much damage on a successful one. The fire spreads around corners, and it ignites flammable objects in that area that aren't being worn or carried