Plants vs. Zombies, D&D-style

Wednesday night I ran an experiment that I have been mulling over in my head for months... I was finally inspired to take action based on this post from Vanir over at Critical Hits. I created a D&D encounter based on PopCap's tower-defense game, Plants vs. Zombies. If you are unfamiliar with the original video game, I'm not going to explain it here. I recommend you check out the free online version at PopCap.

So, how did this work in D&D?

The Set-up:
My players found refuge in an undead-infested wilderness at the home of a druid named Mad Dav. When they arrived, he was frantically setting up for a protective ritual at his shrine to Obad Hai (nature god), but needed more time to prepare. The undead were just moments away and he needed the players to hold them off long enough for him to complete his protective spell.

The playing field:
The undead were approaching through Dav's vineyard. This consisted of 5-foot wide rows of dense vines (essentially acting as walls) separated by 15-foot wide furrows. This set up the controlled rows that would funnel the baddies along in a straight line, while still allowing the use of different-sized plants and undead.

The Plants:
The players were each given a pouch containing seeds for several of Dav's special quick-grow plants. There were 5 varieties in the pouches that the players could choose from. Each had a different ability and a set Challenge Rating (CR). The CR was my ad hoc key to quickly resolving combat and a number of other mechanics for the encounter. More on that later. Here's the specific roster of plants.

• CR2 Slinging nettles (based on Needlefolk from the 3.5e Monster Manual 2) These had a basic ranged attack.
• CR6 Assassin Vine These would choke 1 enemy per round and slow the progress of any others crossing their space.
• CR6 Tendriculous These had two bludgeoning tendrils that could reach 10 feet and a swallow attack that could reach adjacent enemies
• CR7 Ram Topiary Guardian These could bull-rush an enemy back to the start of the row, or until they hit another enemy... whichever happened first.
• CR8 Treant These big guys could reach 15 feet and deliver 2 powerful attacks per round

Planting the seeds:
The players had to move to where they wanted to plant a particular seed and use a standard action to place it in the ground. It took a full round to become active, after which time it could start attacking. After planting a particular seed, the player rolled a die corresponding to the plants CR. (e.g. d2 for the slinging nettles, D8 for Treants.) The result of the roll was the number of rounds they had to wait before planting another seed of that type. Hence, lower strength plants were more likely to be available quickly.

The Zombies/Bad Guys:
I used a mix of undead and other blighted creatures of the type rampaging across this particular part of my game world. Again, the CRs are important.

• CR1/2 (round up to 1) Zombies basic, slow moving melee enemy
• CR1/3 (round up to 1) Skeletons basic ranged enemy
• CR3 Ghast faster, more powerful melee enemy
• CR5 Tainted Ogre large, tough enemy with a 10 foot reach
• CR8 Mohrg (I forgot to put any of these into play, but the plan was that they would move out and spawn zombies)
• CR9 Huge Taint Elemental Big baddie with a 15 foot reach

I was really glad I limited the types of units on each side to just a few different types. It helped keep things manageable. I also selected units to offer a variety of attack modes, sizes and reaches.

Combat:
The premise of Plants vs. Zombies only really works if you have tons of plants fighting tons of zombies. For a tabletop game, this means you need to resolve combat FAST or slip into horrible, draggy boredom. I came up with some very fast and loose combat rules based on each creature's CR. The basic premise is as follows:

If a higher CR creature attacks a lower CR creature, it knocks the lower CR creature out of the game. The caveat being that each creature gets only a certain number of attacks per round.
If a lower CR creature survives to hit a higher CR creature, it deals 1 point of damage to the creature. Each creature could survive (you guessed it!) a total amount of damage equal to its CR. This way, a sufficient mob of low end baddies could take down even tough plants, and vice versa.

Gameplay:
I also had to add some elements to how each round played out. I basically divided each round as follows:

1. Players move, plant seeds and take other actions.
2. Plants attack if targets are in range
3. Existing undead move and attack
4. New undead appear and attack if possible
5. Freshly planted seeds become active for the next round

During the planting and seed activation process, I had all my players act simultaneously to speed things up. I then went row by row to all the plants with targets in range and had the players select which targets were being attacked if there were multiple options.

Players had the option to use spells or things against the baddies rather than planting more plants. They also had a couple NPC clerics with them who could help turn undead and three NPC paladins who could eliminate the front ranks of baddies in a mounted charge down a row.

The players' impenetrable wall of plants bars the press of undead

We went through 6 or 7 rounds of combat over the course of an hour despite a whole lot of pieces on the board, so I felt like the speedy combat worked well. My players said they enjoyed the encounter, but mentioned that they didn't feel like the undead were ever on the verge of breaking through. I think I didn't throw enough at them early on... plus they were hasted, and so planting two plants a round. They managed to turtle up pretty quick.

The Out:
Because this was an experiment, I thought it was especially important to have a guaranteed way to end it in the event that things went horribly wrong or became horribly tedious. In this case, Mad Dav completed his ritual. This caused his tree/shrine to glow with a blinding light that melted the remaining undead and caused a burst of growth in the surrounding plants, sealing the area from further intrusion.