You can have more than seven cards in hand at any time, but you have to discard down to your maximum hand size during your cleanup step at the end of your turn
A players party includes up to one each of Cleric, Rogue, Warrior, and Wizard
It's great against flying 1/1 tokens
You can counter a background when its cast just like you could with any other enchantment, and the same goes for destroying them
Trading in 3 mana (2 to activate and the opportunity cost of tapping Fountainport for colorless) and a token for one card isnt the most efficient sac-for-card trade that there is, but youre paying a tax for the modality of all the other abilities and the fact that its a land, not a creature or something
If you cast a spell for which mana may be spent as though it were mana of any color, you may cast it for Leyline of Mutation's second ability's alternative cost and still spend mana as though it were mana of any color