A good rule of thumb is that bulk cards are worth about 10% of the value of individual cards in the same set
It'll just be a matter of experimenting to find the right combination
Mentor is an ability that triggers when it attacks, and it allows you to put a +1/+1 counter on another attacking Creature that has less power than it
I'm not sure if it was restricted out of fairness, or if they actually thought the card was overpowered at 2 mana (can't imagine the thought process, when crusade and bad moon were fine, but then, they restricted gauntlet of might, so maybe they didn't like red guys getting pumped!) Rukh egg looks fine today, maybe even pretty weak
Sure theres instant win combos, such as Quest for Pure Flame, but theres also fun with planeswalkers, proliferate, or cards that put counters everywhere
Since these lands will be played in any mono-colored deck and even two-color decks depending on the deck, I can see always needing them