Ever an opportunist, here's how to convert D&D 5e Monsters to your Into the Odd game.
HP: 1hp per HD. Maximum of 30.
Armour: Noted Armour grants Armour 1, and any extra noted extreme resilience boosts this to 2. Being Large adds a further point of Armour, being Huge adds two, to a maximum of 3.
STR and DEX: These scores are directly transferable. Maximum of 20.
WIL: Use CHA. Maximum 20.
Attacks: Start at d6. Increase by 1 die for each size category above medium and a further step if they wield a heavy weapon. For example, a large creature with a heavy weapon gets 2 increases, from d6 to d8 to d10. No multi-attacks.
Replace Advantage/Disadvantage and Vulnerability/Resistance with Enhance/Impair respectively. Abilities that grant extra damage or protection also use these two qualities as appropriate.
Advantage/Disadvantages on certain saving throws (e.g. Dwarfs vs Poison) can grant more interesting, outright immunities, or generally just be handled in a better way (e.g. Dwarfs are immune to natural poison, or only feel minor versions of the effects on a failed Save).
Make their description scarier.
Example (trimmed down from the full MM entry to the stuff we need)
D&D 5e Adult White Dragon
Armor Class 18 (natural armour)
Hit Points 200 (16d12 + 96)
Str 22 Dex 10 Con 22
Int 8 Wis 12 Cha 12
Ice Walk: The dragon takes no penalty to speed while traversing ice or snow.
Bite: +11 to hit (reach 10 ft.; one creature). Hit: (2d10 + 6) piercing plus 1d8 cold damage.
Frightful Presence: All within 120 Feet. DC14 WIS Save or be Frightened for 1 Minute.
Cold Breath (recharge 5-6): 60ft Cone. 12d8 Damage. DC19 CON Save for half damage.
Into the Odd Adult White Dragon
STR 20, DEX 10, WIL 12. 16hp, Armour 3, Bite (1d12).
Wants to hunt big prey, and keep its lair hidden from greedy explorers. Effortlessly crosses ice and snow. Breathes freezing cold for d10 Damage to all in the blast, freezing any liquids and creating an icy surface.
Want to convert Into the Odd monsters over to your D&D 5e game? Clearly there's been a mistake. Give it some more thought while you run another Into the Odd game.