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.
Impossible
Complete Islands you get 100 credits for each island
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.
That's the only two ways.
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
There is no way to get more points besides buying and finishing islands.
If you solve them you get 100 for every island. You can also finish the games in the store for more credits.
You can earn 100 free credits for completing an island, but each island only once. You get 25 credits for signing up on Poptropica, and a possible 50 for registering your e-mail with the site. You can earn 50 credits for the free games Haunted House and Earth Day (in the Store), and for Dr. Hare's Secret Lab (which costs 250 credits to play, the main draw being the pink rabbot armor).
Not any that are currently known (as of December, 2009, these are the only ways).
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.
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.