D&D 5E What creatures would you use for this...

[Shiroiken]

Most humanoids fit the mold, particularly using the NPC statblocks. While I really like bullywugs and undead, another option would be mephits as an elemental incursion. The elite force could be some mid-level elemental like gargoyles led by an actual elemental.

 

[Deset Gled]

What creature/monster types would you use against a party of 3-4 adventurers (within the bracket of 4th-6th level-ish), who had to defend a farmhouse against waves of attackers and any advice of how you would run it?



The farmhouse is by a small river with a waterwheel connected and there is a bridge that goes across to the house. There are open fields and a forest where the majority of the attacks are coming from and I envisage a monster Special Forces attack from the river or bridge at some point during the night.

The first thing that came to my mind based off your description was ants: ERBzine 3299: Leiningen Versus the Ants Old school, 1938 style.

I would start with a small swarm (use whatever insect you prefer, probably nothing that flies given the group level), then a handful of small vermin, then some medium sized ones, increasing size with each wave until you end with the queen.

If you want to be really tricky, reverse the order. Start with one of the larger sized vermin as a scout, and make it easy. Then a handful of smaller vermin, followed but overwhelming numbers of swarms. Make them to fear large numbers of small things more than one big one. If you go this route, make sure you give them plenty to tools in the farmhouse to do makeshift area attacks (barrels of oil, etc), and also give them tools to use the river defensively.

 

[Tonguez]

My default was going to be undead but ooh Bullywugs! I can see them stealth-swimming and using the waterwheel to get to the roof while the diversion of the giant toads or whatever try to attack from the front.

yep, Bullywugs climbing the waterwheel was exactly the image I envisioned, plus Bullywugs are a great but underutilised creature so PC dont expect them to leap into battle

 

[Fifinjir]

Blights are very plant-y and forest-y, and can cause an extra problem if they can turn the crops into more blights.

 

[Bill Zebub]

Zombie bullywugs.

 

[Redwizard007]

Blights are very plant-y and forest-y, and can cause an extra problem if they can turn the crops into more blights.

Blights led by an evil druid.

Lizardfolk, sahuaghin, locathah, merrow, centaurs, tabaxi, kenku, humans...

 

[MechaTarrasque]

I always like to throw in a slaadi to spice up bullywugs.

 

[Brotton Goodfellow]

Giant ants and Ankhegs. Some ants are 1 hit mooks, others armoured warriors, others spit acid.