One of the best ways to make encounters memorable is by creating great D&D monsters monsters. It is often advisable to use multiple types of monsters to create a more dynamic situation for players. Giving them some archers, a magic user, and a couple of soldiers to deal with will force them to make choices. But sometimes you just want to throw one nasty creature at them that will take all the brawn and brainpower to defeat.
This library will contain all types of monsters, and it will grow over time. So definitely check back in once every while to see if the library has updated.
HBC: Homebrew D&D Monsters
I love making custom monsters. Usually I use ‘Matt Colville’s Action Oriented Monster-rules’ and ‘Zee Bashew’s rules for making monsters more Witchery’. You can easily adapt the monsters for regular D&D 5e by simply ignoring the extra stats and treating the ‘villain actions’ as ‘legendary actions’. But I would absolutely try to work with the aforementioned rules. They add a lot in my opinion.
Here is an overview of all the HBC monsters in this library. Scroll down further if you want a quick impression of each monster.

Forest Fiend
Inspired by the ‘Fiends‘ from The Witcher 3 and the Jötunn of Norse folklore, this big elk-like creature is said to be a mythical protector of the forest. Perhaps it’s no more than some evil being spawned from another dimension. Whatever this homebrew monster is in your universe, it’s a hulking mass with antlers that will dash, smash, and crash into your players. For the complete stat block and strategies, read more.

Saurian
Inspired by the saurians from Dragon’s Dogma, these creatures are intelligent yet ferocious lizardmen. These creatures usually reside somewhere near water, like a riverbank. They work together in a pack, so make one saurian the leader with villain actions (and perhaps some extra HP). The rest can have the same stat blocks and functionalities. Be careful with adding too many, they are resilient if the players aren’t aware of their weaknesses. Click here to read more.