Such small reskins are often all we need. In many cases, this advice alone is enough to serve as a monster template.
Need a flying monkey? Consider a baboon with wings and a flying speed. Need a fiery phoenix? Take the giant eagle or roc, give it immunity to fire, and allow it to deal fire damage with its attacks. The 'Modifying a Monster' section in Chapter 9 of the Dungeon Master's Guide offers excellent advice for modifying monsters to suit the story we have in mind:
Frankly, as a proponent of lazy DMing, that's not a process I recommend. On the very far end of this spectrum we might create an entirely new monster from scratch. We might change a handful of mechanics, giving our fire giant wight necrotic damage instead of the fire damage it might do. We might change a monster's type, such as creating a fire giant wight by giving the fire giant the undead type. We might simply call one monster by another name and description, called reskinning monsters.
There's a wide range of ways we can change up or create new monsters in D&D. New to Sly Flourish? Start Here! Mashing Up Monsters: Using D&D Monster Stat Blocks as Templates
