There are also some enchantments that randomly show up and having a maindeck answer to them is big
If this creature's controller can prevent it from being blocked and can put at least one merfolk into play each turn, it can effectively be used to chain countless turns together, winning the game for its controller
You can tap any three untapped artifacts and/or creatures you control, including Warden of the Inner Sky itself and other creatures you haven't controlled continuously since the beginning of your most recent turn, to pay the cost of Warden of the Inner Sky's activated ability
The Lander tokens also allow you to dip into a third color, though I expect red-green to skew more aggressive than green-blue
It's the best way to get playing, and if you're polite and just starting out, you may be able to borrow a Commander deck, just remember to stay respectful, set aside the Commander before you shuffle, and learn