I had this in my 360 cube in the past, at the time the card was intended to be a payoff for a loam engine based Jund or Golgari deck, alongside effects that let you discard extra (land) cards for value, like
wild mongrel and
jaya ballard, task mage (I can't promise this second one was a smart idea but it was a pet card for awhile) and effects that let you do something with the worm tokens for value (
nantuko husk etc.)
| How many Worms does it usually make the first time it is cast?
I think this depends heavily on when you find it and how all-in the land package is - In a 360 with double fetches (and 4 wastelands!) like I had, it's really easy to get 2 or 3 lands in the yard by turn 5, especially if you've got something early with a discard outlet on it. Generally speaking it feels really bad to actually cast this for less than 3 worms, but I've seen retrace into two worms into swing a nantuko husk to close out the game, so sometimes only getting a few is ok. (compare to lingering souls, which gives you 4 1/1 fliers for 5CMC - the value in Worm Harvest is that you can do it a lot.)
the fewest I ever saw it make was 2. generally players wouldn't cast it for 1 worm token. the most I ever saw on initial cast was 6(!) but it was also a late top-deck in that game.
| Is it only scaling based on the lands it's using to cast it using retrace or are decks running this generally able to fill additional lands to yard?
I've only seen it used in decks that had ways to get land into the yard beyond the retrace. I generally support self-mill / discard in this corner of the color pie however, so my experience is not exhaustive in this case. If you're in B and/or G in my cube you're probably discarding or milling for value which will put lands in the yard. If you're running Looting effects in R/U these also tend to throw extra lands in the yard as well.
| Is it primarily a dredge card or can more traditional golgari "rock" style decks use it without too much issue?
I *think* a general rock deck can use it as a value / chump blocker engine late game (it gives you something to do with extra lands, if your cube ends up in top deck wars, this is a sweet way to try to win those.) - if you play it in Jund it's spicy as hell after a wildfire, but to make those plays work on curve you'd generally need more artifact ramp than I think a lot of riptidian cubes run these days (certainly more than I do, anyway).
I think it's actually also interesting in a go-wide tokens deck using white anthem effects with green token makers, although the triple hybrid cost means it's much more common in a GB or GBx deck than a GW deck.
| Is it's initial cast generally from hand or from in the yard?
It feels *Way* better casting it from the yard, but assuming you've been dumping lands into the yard somehow on the way to 5 lands in play, there's nothing wrong with initial casts from the hand, I think this depends on when you draw it. It's an excellent card to pitch in the first couple turns of the game, so decks with access to ways to pitch cards for value early are going to be happy to do that.
| Repetitive Gameplay
I cut this for cube complexity reasons (it was my only retrace card and my usual players at the time were not generally very experienced magic players, people would sometimes forget they could use it, etc.) I think like most repetitive value effects that this is generally fun for Hero and mixed for Villain. Dredge decks sort of already have this "problem" in cube where they can feel like infinite value engines that don't play 'fair' economics because their graveyard is almost a second hand - but Worm Harvest is not generally the most egregious version of those sorts of effects - and even making 3,4,5 or more vanilla 1/1s three turns in a row are theoretically possible to answer (pyroclasm) or race (big flying vigilant baneslayers) in most cubes.
| other thoughts:
I think this card is an example of a deep card in cube: it represents the intersection of a number of themes (which are generally all easy to support: go-wide tokens, discard, lands, sacrifice) it's hybrid colored so appeals to the widest possible number of drafters, and its an effect that rewards carefully constructing the rest of your draft pool around it.
However, I also think that it's not a card you can just drop into any cube and see dividends: it's fairly slow, it's only really good if your GB corner decks can make games go long enough to build up value, and it can lock-up a game without actually *winning* the game, which is generally when the feel bad moments start. (the worst experience in limited in my opinion is knowing you basically *can't* win, but it not actually being a foregone conclusion that you can't.)