Some Killer Pumpkins

Smaller pumpkins might attack as a swarm?
Enough killer pumpkins could pull a cart
A killer pumpkin could be a mount for other creatures

Killer Pumpkin
Nuetral or evil plants
AC+3 HD d4 Bite d3 Move 6 (hop)
Killer pumpkins are regular-sized pumpkins with a taint of chaos or possibly created by druids to guard locations during certain festivals or just ordinary witches gardens. Look like regular pumpkins but can hop high enough to reach an adult face or clear a fence. They avoid water as they swim poorly but they float. They gibber insanely, roll their eyes and make peculiar expressions. They are edible and technically vegetables and taste sweet and delicious. They prefer to work in groups as a single one will be eaten by farm animals. If you are in a pumpkin patch and they are asleep they look like normal pumpkins and may make a surprise ambush attack before the initiative. They can eat more flesh than they ought to for size and will gain maximum HP if eat their weight in flesh 

1in4 explode with fire on death for a d4 damage to all in a 3m circle 
1in6 eventually re root themselves and grow a humanoid body (pumpkin abjumans)
1in6 can spit a d6 fire range 6, they also have glowing flickering eyes
1in10 can project eerie orange light from eyes at will to highlight a target
1in10 have bat wings and can fly
1in10 if you eat a pumpkin save or turn into a pumpkin-headed abhumanoid next full moon
1in12 can cause fear in 1HD or less creatures with gaze 3 range save or flee d4 rounds
1in12 are intelligent and hurl vile abuse and accusations at enemies or anyone
1in12 have vine tendrils that can make a grapple attack, once held the pumpkin hits automatically each round
1in20 are pumpkin kings AC+4 HD4 Bite 2d4 Move 12 and command lesser pumpkins
1in20 pumpkins can open their lids and maybe homes to giant rats, bats or other smallish creatures that may aid them in combat. A group of pumpkins might keep a swarm of rats
1in20 if they don't move or make other attacks can fire a magic missile per round. Make good guards and may be placed over a door or on a fencepost. These tend to be smarter ones who can discriminate wh they attack

d12 Killer Pumpkin Plots
1 This year some goblins planted killer pumpkins in the local village gardeners and they need culling
2 A sinister witch has been reported but all fear her pumpkin patch
3 The annual harvest festival has a wagon load of the finest pumpkins coming for the festivities but an evil wizard has replaced with evil pumpkins and has taken the real ones for himself
4 Several gardeners have vanished and nobody saw them leave
6 A druid made angry by loggers and fur trappers has let killer pumpkins loose in their camps and driven the workers from the forest
7 A dark elf has been leaving killer pumpkins in villagers gardens. Stop the evil elf and burn his evil garden
8 The great and terrible pumpkin spirit has been angered by a new vegetable in the village and finally will be angry enough to send an angry pack of pumpkins
9 An alchemist has been dumping failed potions and now killer pumpkins have been coming from the now-abandoned pumpkin farm downstream
10 A swarm of bat-winged pumpkins has been menacing the town by night and eating local cats
11 A wicked miser and pumpkin farmer seems to have been absent, could someone visit their isolated farm and check upon them. His soul is now in the body of a king pumpkin and he plans to lead them to the village to eat everyone and steal their pennies
12 A witch in a chariot pulled by pumpkins comes to town. She says villagers have one day to prepare her a feast and some babies or she will unleash her orange minions