If you start off with no credits, then you have to buy the credits. I think $20 gets you 2000 credits. If you already have, let's say, 500 credits, than you have to buy more credits, also. You would need 1,500 credits, and 1,500c=$15.00
You receive 100 Poptropica credits when you receive the Island Medallion for any given island (50 credits for completing Haunted House). If you look in the item bag for each island, you should see the Medallion. If it's not there, you didn't finish the island and didn't get your 100 credits.
(see solutions at the related question below)
Once you finish all the islands, and Haunted House, there is no way to earn more free credits until another island comes out.
There is no way to get free credits without completing islands, except for the free Earth Day game (50 credits) in the Poptropica Store.
You can buy them at the store
That's the only two ways.
Not any that are currently known (as of December, 2009, these are the only ways).
Complete Islands you get 100 credits for each island
The only way to get free Poptropica Credits is to complete islands (or the three games in the Store). You also get 25 credits for signing up. Otherwise, adults can purchase credits or memberships through the store.
If you solve them you get 100 for every island. You can also finish the games in the store for more credits.
There is no way besides winning them or buying them. Unless you can get someone else to play it for you. You can also earn credits for beating Earth Day or the Haunted House, which are mini-quests available in the Poptropica store.
The only two ways are completing islands (and Haunted House and Earth Day), or by buying them. That's the arrangement. There are no tricks, shortcuts, or secret methods.
You get 25 credits for signing up, and you can earn 50 by playing the free game Earth Day, or the Haunted House game, available in the Poptropica store. The only other ways to earn credits are by completing islands or by an adult purchase of credits or gift cards.
There is no other way....I don't think. The only 2 ways I know of is: Winning islands and buying them in real life.
Impossible
You can enter someone else's Multiverse room by invitation, at no cost to you. You can get multiverse with no credits if you are a Poptropica member. Paid monthly members can use anything in the store without spending credits. But they cannot keep the items used if they stop their membership.
you can't unless it is a sneak peak