Grumgully, the Generous is probably the most obvious example: we make Spirits, they auto-get a +1/+1 counter, and therefore they'll get more because they're modified
A: When something adds mana to your mana pool, you have to spend it by the end of the current phase, otherwise you get mana burn, and lose life for all unspent mana
Avalanche Caller can animate your snow lands into 4/4 elementals, while Boreal Outrider makes your creatures enter with a +1/+1 counter if snow mana was used to cast them
We can expect the value of showcase cards to be at least 30% more expensive than the normal version, and thats being conservative
Some collectors perceive Beckett as being stricter in certain aspects of grading, such as centering and surface condition