I don't want to call them not fun, since they usually are fun
Long Feng, Grand Secretariat Long Feng, Grand Secretariat is a perfect advisor to remind you how easy it is to send your lands to the graveyard even without earthbending (ahem, fetches)
This provides some decent fixing, but filter lands are a little to inefficient to be great
As a very general rule for Limited, I would look to play something like this: 1 mana: 02 2 mana: 46 3 mana: 35 4 mana: 24 5 mana 13 6+ mana: 02 That's far from set in stone, but it's a good place to start
Like most Magic: The Gathering cards, the value of Serra Avenger depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Time Spiral Remastered)
How can location cards combo with characters