Normally, saving anything to a blockchain requires a fee for spam protection. However, a common method to fund an online game is with the freemium model. New players can play for free to learn the game and see if they like it, while premium players pay a fee to get access to new content / new skills / new activities.
Some suggestions
it's open-source software, so players could run a demo locally, but this means they are not playing the proper game.
the devs host a demo server that's reset.
players could perform some task to get free credits from the dev. Perhaps assist in marketing and then the devs provide some tokens from their own stash. The more manual this is, the worse it will scale. Players could provide email addresses of friends in order to earn credits: it is a form of marketing that's easy to automate, but not poor for privacy.
devs can also provide credits from their own stash, but this is not necessarily sustainable and possibly hard to make sybil resistant (unless doing KYC).
Allow for gifting of credits (player to player).
Allow players to pay a monthly sub with in-game work. They collect tokens from in-game activities but need to pay some of this to the devs, or potentially burn it. A problem here that free actions are a problem for spam.
Is there a reliable way to prove that a player runs a full-node? If so, perhaps they should be credited with a number of actions (or tokens) on a pro-rata basis (thinking on Filecoin).
Early levels free, but later levels cost
New players could potentially play a free version that's centralised, or on a side-chain. In either case, the considerations for spam protection will be different. The sidechains could be located in strategic geographic locations too. As a related aside, sidechains could perhaps be used for instancing.
In this free version, new players will get access to very limited content. Perhaps only access to levels 1 - 10. If they want to pay then they can access the full content in the decentralised game. Any items gathered in the free version could be burnt and that value transferred to the full game.
New premium players would have the option of starting from level 10 and can have a start set of items. This means a premium player is just paying for convenience (a jump start).
F2P Pool of funds
Potentially there is a pool of funding that players could contribute to that allows new players to play for free, but naturally there needs to be a limit to their actions and there needs to be considerations for sybil resistance.
The following link is an interesting find from @Codie-Petersen.
It has some research on revenue generation and freemium models in traditional gaming.
Make it obvious that players can spend their money. Not always obvious to players.
A free trial is important to get the hook, but ultimately it is important to have end-game content (Conan and SWTOR sucked at this early on, but WoW apparently did it well).
How to do free-to-play in a blockchain game?
Normally, saving anything to a blockchain requires a fee for spam protection. However, a common method to fund an online game is with the freemium model. New players can play for free to learn the game and see if they like it, while premium players pay a fee to get access to new content / new skills / new activities.
Some suggestions
Early levels free, but later levels cost
New players could potentially play a free version that's centralised, or on a side-chain. In either case, the considerations for spam protection will be different. The sidechains could be located in strategic geographic locations too. As a related aside, sidechains could perhaps be used for instancing.
In this free version, new players will get access to very limited content. Perhaps only access to levels 1 - 10. If they want to pay then they can access the full content in the decentralised game. Any items gathered in the free version could be burnt and that value transferred to the full game.
New premium players would have the option of starting from level 10 and can have a start set of items. This means a premium player is just paying for convenience (a jump start).
F2P Pool of funds
Potentially there is a pool of funding that players could contribute to that allows new players to play for free, but naturally there needs to be a limit to their actions and there needs to be considerations for sybil resistance.