Example of converted Pathfinder monster - as here, the CR generally works out 2-3 higher:
5e Monsters - Rune Giant
This giant’s skin is black and pitted, like roughly cast iron, and etched with glowing red runes.
Rune Giant CR 20
LE Gargantuan humanoid (giant)
Init +0; Senses low-light vision; Passive Perception 21
Proficiency +6
Str 30 (+10), Dex 11 (+0), Con 24 (+7), Int 14 (+2), Wis 21 (+5), Cha 18 (+4)
AC 20
hp 405
Good Saves STR +16 CON +13 INT +8 WIS +11
Immune cold, electricity, fire
OFFENSE
Speed 50 ft.
Melee Greatsword (2 attacks) +16 dam 45 slashing (crit 67 slasing on 19–20) and an SML target is Pushed back 10' and knocked prone.
Ranged Javelin +16 dam 31 piercing (crit 46 piercing/19-20) plus 21 lightning damage; range 60'/240' and a SML target is Pushed back 10' and knocked prone.
Space 20 ft.; Reach 20 ft.
Equipment: Greatsword, 2 javelins.
Special Attacks command giants, runes, spark shower
Spell-Like Abilities (Spell Save DC 18; Spell Attack +10)
At will—charm person; suggestion
3/day—mass charm monster; dominate person
1/day— true seeing; air walk
STATISTICS
Skills Athletics +16; Craft +8; Knowledge (history) +8, Knowledge (nobility) +8, Perception +11
Languages Common, Giant, Terran
SPECIAL ABILITIES
Command Giant
Giants have disadvantage on saves vs charm or compulsion effects used by rune giants.
Runes
Whenever a rune giant uses its spark shower or spell-like abilities, it can cause the runes on its body to flash with light. All creatures within 10 feet of the giant must make a DC 18 CON save or be Blinded until the end of their next turn.
Spark Shower
As an action, a rune giant can cause a shower of sparks to erupt out of one of the runes on its body. These sparks function as a 30-ft. cone; 45 fire and 45 electricity damage; DC 18 DEX save half; recharge 5-6.
Legendary Resistance 3/day: The Rune Giant can choose to pass a failed save.
Legendary Action 1/turn, max 3/round: At the end of another creature's turn the Rune Giant may make a Greatsword attack or use Spark Shower (if available).