Yeah, that's nice.
What I really need are 5e rules clever snippets of things like
-Pair these monsters together because complimentary reason X: 3e Medusa, Grimlock(blind)
-Put this kind of trap in a room like this, or an encounter with these monsters
Need meaty 5e DM content, less time to adapt things lately.
Flameskulls are really good minions for anything immune to fire and/or evasive They're basically animated hand-grenades. They maintain usefulness against high level adventures since their CR is low enough to use them in a great enough number that a couple fireballs going off in the first round will challenge a level 12+ group, and after the initial explosion, magic missile is guaranteed damage. Flight and shield can make them difficult to hit, but their low HP makes them manageable when focused on.
Intellect Devourers with Mind Flayers are a bit of a gimme, and very lethal for their CR.
Xorns are amazing bloodhounds for anything that could be expected to control an earth elemental. Treasure sense means they can track adventurers easily.
Onis with their at-will darkness are great with devils since most devils can see through magical darkness.
The Helmed Horror is an amazing minion to anything you want to use that has a mass control effect and/or spell-based area damage due its long and customizable list of immunities.
Flesh golems heal from lightning damage, so pair them with things that aren't afraid to toss lightning bolt/chain lightning/call lightning around. Or make a blue dragon necromancer via the innate spellcasting variant for dragons.
It might not be RAI, but RAW a dryad can move between a treant's animated trees, and the treant can stay still to avoid revealing itself even as the animated trees attack.
Any crappy low CR minion can still use the help action to give advantage to its stronger master.