Wyvern

Wyvern hatchling:

Small Dragon, unaligned   Armor Class 11 (Natural Armor)
Hit Points 7 Speed 10ft.,
Initiative +0 Fly 40ft   STR 11 (+0) INT 2 (-4)
DEX 10 (+0) WIS 8 (-1)
CON 8 (-1) CHA 2 (-4)
  Bite [+0] 1d4
Stinger [+0] 1d4 (DC 10 Con saving throw; 1d6 Poison damage)  

Wyvern Wyrmling:

Medium Dragon, unaligned   Armor Class 12 (Natural Armor) Speed 15ft
Hit Points 27 Flight 60ft
  STR 15 (+2) INT 3 (-4)
DEX 10 (+0) WIS 10 (+0)
CON 12 (+1) CHA 4 (-3)
  Bite [+4] 1d6+2
Stinger [+4] 1d6+2 (DC 12 Con saving throw; 3d6 Poison damage)  

Wyvern: Youngling:

Large Dragon, unaligned
  Armor Class 13 (Natural Armor) Speed 20ft
Hit Points: 80 Flight 80ft
  STR 19 (+4) INT 5 (-3)
DEX 10 (+0) WIS 12 (+1)
CON 16 (+3) CHA 6 (-2)
  Multiattack. The wyvern makes two attacks: one with its bite and one with its stinger.
Bite [+5] 2d6+2
Stinger [+5] 2d6+2 (DC 14 Con saving throw; 5d6 Poison damage)