Weiley31
Legend
Hmmm...You know, I never really thought of doing an Ogre as a refluffed Firbolg. Now I'm wondering/curious..........hmmm, lets see:
www.dndbeyond.com
Looks at the Stat Block.
--Creature Type: Oni (Giant). Firbolg (Fey-Oriented Giant). Okay: that lines up with their races
--At Will-Abilities: Invisibility(Oni)/Hidden Step racial Trait(Firbolg). Wow, so both have the ability to go Invisible in someway.
--Change Shape Action (Oni)/Firbolg Magic racial Trait: Disguise Self spell. Well, interesting, both have some way of changing how they look to others as well in some fasion.
--Weapon Proficiency: Iron Kanobo (Oni in Japanese Mythology)/Weapon Proficiency: Clubs, Giant-Kin Weapons. Two-Handed Swords (Firbolg in 2nd Edition). And an Odachi is a kind of two handed sword.
en.wikipedia.org
I don't bloody believe it conclusion: The Firbolg IS the option to refluff/go-to if you wanted to play as a Ogre/Oni Mage/Yokai Oni. I always looked at the Orc for that, but I guess this means that the Orc would could be refluffed as the more "Physical" martial type of Oni while the Firbolg would be the refluffed version of the more Mystical/Magical Oni variant. And, I've seen Yokai get listed as Fey before in 5E. Especially with Kobold Press: Both the Kitsune and it's Chinese variant, the Huli Jing, get typed as Fey by them.
I dig/approve it.

Oni
Innate Spellcasting. The oni's innate spellcasting ability is Charisma (spell save DC 13). The oni can innately cast the following spells...

Looks at the Stat Block.
--Creature Type: Oni (Giant). Firbolg (Fey-Oriented Giant). Okay: that lines up with their races
--At Will-Abilities: Invisibility(Oni)/Hidden Step racial Trait(Firbolg). Wow, so both have the ability to go Invisible in someway.
--Change Shape Action (Oni)/Firbolg Magic racial Trait: Disguise Self spell. Well, interesting, both have some way of changing how they look to others as well in some fasion.
--Weapon Proficiency: Iron Kanobo (Oni in Japanese Mythology)/Weapon Proficiency: Clubs, Giant-Kin Weapons. Two-Handed Swords (Firbolg in 2nd Edition). And an Odachi is a kind of two handed sword.

Oni - Wikipedia
I don't bloody believe it conclusion: The Firbolg IS the option to refluff/go-to if you wanted to play as a Ogre/Oni Mage/Yokai Oni. I always looked at the Orc for that, but I guess this means that the Orc would could be refluffed as the more "Physical" martial type of Oni while the Firbolg would be the refluffed version of the more Mystical/Magical Oni variant. And, I've seen Yokai get listed as Fey before in 5E. Especially with Kobold Press: Both the Kitsune and it's Chinese variant, the Huli Jing, get typed as Fey by them.
I dig/approve it.