Sun shining, clouds smiling, climbing down a tree in glee, Sluggy, a happy, purple slug, strolls along to the blood-red, big berry in our yard.
This isn't correct, and not just because of style; there are at least several sentences in here, all mashed together. Plus some smaller issues that I'll get to at the end.
There are two major problems that I see here. The first one is that the description of the environment is inappropriately connected to Sluggy. "Sun shining, clouds smiling" -- these clauses don't describe Sluggy, so they need to be separated from Sluggy. One simple alternative is to just create a new sentence:
The sun was shining and the clouds were smiling. Sluggy, a happy purple slug...
Or, the description of the environment could go in a clause:
Under a shining sun and smiling clouds, Sluggy, a happy purple slug...
There are going to be quite a few commas in that sentence once it's complete, though; it may feel clunky even if it's grammatically correct.
There are other ways to do this, too - but the point is that unless the description applies to Sluggy, the description needs to be separated from Sluggy.
The second problem is that Sluggy is doing two actions in the same sentence: "climbing down a tree" and "strolls along". If you're going to have two verbs in the same sentence, then at a minimum they need to match in tense:
He was walking and talking at the same time.
So at a minimum, Sluggy's two verbs need to match their tense. However, even if the tenses matched, "climbing" and "strolling" aren't really two activities that can be done at the same time. How could Sluggy be climbing down the tree while also strolling to the berry? It sounds like Sluggy would be climbing down first, then strolling to the berry. In that case, these two actions should be two clauses, or two sentences:
Sluggy climbed down the tree with glee, then strolled along...
Now, a few nit-picky things:
- Clouds can't smile. (Of course, if this is an illustrated children's book, they can.)
- "Stroll" is a form of "walk"; slugs don't walk, they "crawl".
- "Stroll" and "glee" also don't really go together. If Sluggy is so intent on getting to the berry, why would Sluggy stroll to the berry? A "stroll" is a leisurely walk; I'm only going to stroll if I'm not in a hurry. If Sluggy is hungry, (s)he probably won't be strolling, even if (s)he's moving slowly.
the blood-red, big berry
The order should be "big, blood-red berry". The order of adjectives matters in English, and size comes before color.
(Source: Cambridge Dictionary.)