World Builder Game Units
This game represented the LEGO Designer Sets (Make &amp; Create) from 2003–2005, and so the majority of models are based on them (WB1 models are from the first and second waves, and WB2 the third wave). As someone who grew up with the game and the Designer Sets as a tween, and still has many of them built to this day, I believe I can answer this question mostly, though there is still some I'm uncertain about which I'll note near the end of my answer.
From WB1 (links point to BrickInstructions.com):

The Snail, Frog, as well as the enemies Crab (of which the Watercrab is a palette swap), Scorpion and Alligator are from 4101 Wild Collection. Step-by-step instructions exist for the Crab, Scorpion and Alligator; the rest are inspirational builds that are simple and therefore should be easy to reverse-engineer. Notably, the Snail, Frog, Scorpion and Alligator can all be built simultaneously from a single copy of the set. The proportions are also all wrong in case that bothers you; namely the Scorpion is monstrously oversized compared to the rest. Or... the proportions could all be just right, depending on your imagination.
I still have my Crab built from 17 years ago, so I hope you'll overlook the dust and grime still on it after a quick clean (click to enlarge):


The Buggy, Dirtbuggy, Forklift and Gas Station are from 4100 Maximum Wheels. Instructions exist for the Buggy's in-game model as well as the Dirtbuggy (which is actually a palette swap) and Forklift. The Buggy's info model is an inspirational build with no step-by-step instructions, and the Gas Station and Marina are different color variations on one inspirational side build seen on the cover art. The decals are exclusive to WB1 — Designer Sets don't have printed elements.
I rebuilt the Forklift a few months ago:
 

The Defender, Treebot and Repairbot are from 4099 Robobots. Instructions exist for the Defender and Treebot but not the Repairbot (you can see it on page 73). I built the Defender and Treebot when I was younger and I have to add that the Treebot is actually depicted in the set as an aquatic robot that operates underwater, and it can be configured to different positions and not just standing upright. Unfortunately, upright its two bottom/hind legs don't support its weight very well, the joints being little more than single-hinge connection points. It works much better on all fours.
As for the Defender, despite what the scale of the in-game models suggests, it is much smaller than the Treebot — though it's got a much bigger brother in 4508 Titan XP. I just went and built the Defender so I could show it to you next to a minifig for scale:


The Bulldozer and Dumptruck are from 4096 Micro Wheels. Instructions exist for both models.

Instructions for the Speedboat can be found in 4505 Sea Machines.

Instructions for the Tyrannosaurus Rex can be found in 4507 Prehistoric Creatures. It is one of the main builds.

Instructions for the Shark can be found in 4506 Deep Sea Predators (the predecessor of 31088 Deep Sea Creatures). It is one of the main builds. I rebuilt it in 2018 when I first exited my Dark Ages with 10404 Ocean's Bottom — here's a photo from my review of the latter:



WB1 units I couldn't identify:

The Steamshovel appears to have a body that's a palette swap of the Forklift's, but the vehicle as a whole doesn't appear to exist in any set. I can't identify exactly which digger bucket it's using so I might try to BrickLink it and see what set it might be. I'm guessing it's unique to the game.

According to Alexander O'Mara, the Robot Lab appears to be a palette swap of an inspirational model from 4098 High Flyers. Not exactly the place I would've looked...

The Guard Tower doesn't bear any resemblance to anything I've seen in a Designer Set or X-Pod (at least, as an owner of the first wave of X-Pods).

The Duck, Fish, Tugboat and Freighter appear to be from LEGO Creator buckets also under Make &amp; Create. They certainly don't have the level of detail or part usage that Designer Set models are recognized for.
I was right: as Alexander confirms, they're from 4028 World of Bricks.


From WB2:

Instructions for the Freezebot can be found in 4881 Robo Platoon (which incidentally was Brickset's random set of the day just last week). It is one of the main builds.

Instructions for the House can be found in 4886 Building Bonanza. It is the main build.
However, despite being based on that same House, none of the other WB2 buildings actually appear in the set, except the Windmill, which only appears as an inspirational model with instructions for the actual mechanism for spinning the sails.

Instructions for the enemy Lion can be found in 4884 Wild Hunters. It is one of the main builds.


Notably, all the Designer Sets in the final wave were given the &quot;new&quot; Creator rebranding later in life. I wasn't there when it happened though — I had just entered my Dark Ages before that, and I never had a chance to own any of the final wave sets. 4886 Building Bonanza remains among my top 10 most wanted sets of all time.
Thanks for the opportunity to take us on a trip down memory lane!