Inspired by the Egg Hunt encounter designed by Drunkens & Dragons, this giant armored spider has two particularly interesting elements:
Every 1d4 rounds, the spider spits out 1d4 teethed pupae, who quickly join the fray. The pupae are low on Armor Class and Hit Points but high on damage, which means PCs are likely to ignore them and focus on the spiders until the pupae get in one or two good hits. By that point there may be an overwhelming number of pupae, depending on how many spiders you include.
This monster introduces a facing mechanic. Due to its chitinous armor and steel-like blades of its forearms, normal weapon damage is halved if the attacks are made against the spider’s side and front. Its bulbous, pupae-filled, pregnant abdomen, however, will take damage like normal.
I ran two of these spiders against a 6th-level party and it was a pretty tough encounter; two of six PCs dropped below 0 Hit Points.
And here are the stat blocks:
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> ## Pregnant Armor Spider
>*Large beast, unaligned*
> ___
> – **Armor Class** 14
> – **Hit Points** 75 (14d10)
> – **Speed** 40 ft., climb 40 ft.
>___
>|STR|DEX|CON|INT|WIS|CHA|
>|:—:|:—:|:—:|:—:|:—:|:—:|
>|14 (+2)|16 (+3)|12 (+1)|2 (-4)|11 (+0)|4 (-3)|
>___
> – **Skills** Stealth +7
> – **Damage Immuinities** poison
> – **Senses** blindsight 10 ft., darkvision 60 ft., passive Perception 10
> – **Languages** —
> – **Challenge** 3 (700 XP)
> ___
> ***Spider Climb.*** The spider can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
>
> ***Web Sense.*** While in contact with a web, the spider knows the exact location of any other creature in contact with the same web.
>
> ***Web Walker.*** The spider ignores movement restrictions caused by webbing.
>
> ***Armored.*** The spider is resistant to slashing, bludgeoning, and piercing damage against the front and sides of the spider.
>
> ***Disgorge Pupae.*** Every 1d4 rounds, the spider disgorges 1d4 teethed pupae.
> ### Actions
> ***Bite.*** *Melee Weapon Attack:* +7 to hit, reach 5 ft., one creature. *Hit:* 7 (1d8 + 3) piercing damage, and the target must make a DC 11 Constitution saving throw, taking 9 (2d8) poison damage on a failed save, or half as much damage on a successful one.
>
> ***Slash.*** *Melee Weapon Attack:* +5 to hit, reach 5 ft., one creature. *Hit:* 9 (1d8 + 5) piercing damage.
___
> ## Teethed Pupae
>*Small beast, unaligned*
> ___
> – **Armor Class** 10
> – **Hit Points** 10 (1d10 + 5)
> – **Speed** 20 ft.
>___
>|STR|DEX|CON|INT|WIS|CHA|
>|:—:|:—:|:—:|:—:|:—:|:—:|
>|14 (+2)|10 (+0)|12 (+1)|2 (-4)|6 (-2)|4 (-3)|
>___
> – **Senses** blindsight 10 ft., darkvision 60 ft., passive Perception 10
> – **Damage Immuinities** poison
> – **Languages** —
> – **Challenge** 1/4 (50 XP)
> ___
> ### Actions
> ***Bite.*** *Melee Weapon Attack:* +7 to hit, reach 5 ft., one creature. *Hit:* 8 (2d6 + 2) piercing damage.