The first wave of amass cards all created a Zombie Army, but with the addition of amass orcs in LTR, the original mechanic was changed to amass zombies. This allows different sets to represent armies that match the flavor of that set
Theres a high upside in participating in the different events Arena has to offer
One example may be "500 assorted commons and uncommons, Mirrodin through Shards of Alara era," "2,000 bulk commons from 2010 onwards" or "1,000 pre-modern bulk commons, uncommons and rares." New players who want to cheaply kick-start their collection can buy these bulk lots and gain countless new cards to play with, as well as explore a wider variety of cards than most Magic starter products provide
1998 - Unglued Frame Unglued was the first Magic set to officially print token cards
They'll try to remove it, but that's what your counterspells are for