Intermediate Blue Dragons, CR 4-8 (D&D 5E)
As written, the lowest two Challenge Ratings for Blue Dragons in the D&D 5E Monster Manual are CR 3 for a Blue Dragon Wyrmling and CR 9 for a Young Blue Dragon. If you need an appropriate boss monster to face off against a mid-level party of 4th to 8th level adventurers, however, you might not want to either allow them simply to slaughter off a Wyrmling or have the next available age of Dragon make short work of them. With that in mind, we have created five intermediate Blue Dragons in order to give storytellers greater flexibility. Note that all of these variants are size Medium and that the Dragon does not become fully Large until it reaches CR 9.
Pre-Juvenile Blue Dragon (CR 4; 6-10 years)
Medium Dragon, lawful evil
Armor Class: 17 (natural armor)
Hit Points: 67 (9d8+27)
Speed: 30 ft., fly 60 ft.
STR DEX CON INT WIS CHA
18 (+4) 10 (+0) 16 (+3) 12 (+1) 11 (+0) 15 (+2)
Saving Throws: Dex +2, Con +5, Wis +2, Cha +4
Skills: Perception +4, Stealth +2
Damage Immunities: Lightning
Senses: Blindsight 10 ft., Darkvision 70 ft., passive Perception 14
Languages: Draconic
Challenge: 4 (1,100 XP)
ACTIONS
Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 9 (1d10+4) piercing damage plus 4 (1d8) lightning damage.
Lightning Breath (Recharge 5-6). This Blue Dragon exhales lightning in a 35-foot line that is 5 feet wide. Each creature in that line must make a DC 13 Dexterity saving throw, taking 27 (5d10) lightning damage on a failed save, or half as much damage on a successful one.
Juvenile Blue Dragon (CR 5; 11-20 years)
Medium Dragon, lawful evil
Armor Class: 17 (natural armor)
Hit Points: 82 (11d8+33)
Speed: 30 ft., fly 65 ft.
STR DEX CON INT WIS CHA
18 (+4) 10 (+0) 16 (+3) 12 (+1) 11 (+0) 16 (+3)
Saving Throws: Dex +3, Con +6, Wis +3, Cha +6
Skills: Perception +6, Stealth +3
Damage Immunities: Lightning
Senses: Blindsight 15 ft., Darkvision 80 ft., passive Perception 16
Languages: Draconic
Challenge: 5 (1,800 XP)
ACTIONS
Multiattack. This Blue Dragon makes two attacks: one with its bite and one with its claws.
Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 10 (1d12+4) piercing damage plus 4 (1d8) lightning damage.
Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6+4) slashing damage.
Lightning Breath (Recharge 5-6). This Blue Dragon exhales lightning in a 40-foot line that is 5 feet wide. Each creature in that line must make a DC 14 Dexterity saving throw, taking 33 (6d10) lightning damage on a failed save, or half as much damage on a successful one.
Pre-Adolescent Blue Dragon (CR 6; 21-35 years)
Medium Dragon, lawful evil
Armor Class: 17 (natural armor)
Hit Points: 97 (13d8+39)
Speed: 35 ft., fly 70 ft.
STR DEX CON INT WIS CHA
19 (+4) 10 (+0) 17 (+3) 13 (+1) 12 (+1) 16 (+3)
Saving Throws: Dex +3, Con +6, Wis +4, Cha +6
Skills: Perception +7, Stealth +3
Damage Immunities: Lightning
Senses: Blindsight 20 ft., Darkvision 90 ft., passive Perception 17
Languages: Draconic
Challenge: 6 (2,300 XP)
ACTIONS
Multiattack. This Blue Dragon makes two attacks, one with its bite and one with its claws.
Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6+4) piercing damage plus 4 (1d8) lightning damage.
Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 8 (1d8+4) slashing damage.
Lightning Breath (Recharge 5-6). This Blue Dragon exhales lightning in a 45-foot line that is 5 feet wide. Each creature in that line must make a DC 14 Dexterity saving throw, taking 38 (7d10) lightning damage on a failed save, or half as much damage on a successful one.
Adolescent Blue Dragon (CR 7; 36-55 years)
Medium Dragon, lawful evil
Armor Class: 17 (natural armor)
Hit Points: 112 (15d8+45)
Speed: 35 ft., fly 70 ft.
STR DEX CON INT WIS CHA
19 (+4) 10 (+0) 17 (+3) 13 (+1) 12 (+1) 16 (+3)
Saving Throws: Dex +3, Con +6, Wis +4, Cha +6
Skills: Perception +7, Stealth +3
Damage Immunities: Lightning
Senses: Blindsight 25 ft., Darkvision 100 ft., passive Perception 17
Languages: Draconic
Challenge: 7 (2,900 XP)
ACTIONS
Multiattack. This Blue Dragon makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8+4) piercing damage plus 4 (1d8) lightning damage.
Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 8 (1d8+4) slashing damage.
Lightning Breath (Recharge 5-6). This Blue Dragon exhales lightning in a 50-foot line that is 5 feet wide. Each creature in that line must make a DC 14 Dexterity saving throw, taking 44 (8d10) lightning damage on a failed save, or half as much damage on a successful one.
Very Young Blue Dragon (CR 8; 56-75 years)
Medium Dragon, lawful evil
Armor Class: 18 (natural armor)
Hit Points: 136 (16d8+64)
Speed: 35 ft., fly 75 ft.
STR DEX CON INT WIS CHA
20 (+5) 10 (+0) 18 (+4) 14 (+2) 13 (+1) 16 (+3)
Saving Throws: Dex +3, Con +7, Wis +4, Cha +6
Skills: Perception +7, Stealth +3
Damage Immunities: Lightning
Senses: Blindsight 30 ft., Darkvision 110 ft., passive Perception 17
Languages: Common, Draconic
Challenge: 8 (3,900 XP)
ACTIONS
Multiattack. This Blue Dragon makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 14 (2d8+5) piercing damage plus 5 (1d10) lightning damage.
Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 10 (1d10+5) slashing damage.
Lightning Breath (Recharge 5-6). This Blue Dragon exhales lightning in a 55-foot line that is 5 feet wide. Each creature in that line must make a DC 15 Dexterity saving throw, taking 49 (9d10) lightning damage on a failed save, or half as much damage on a successful one.