Not only does it protect our board against wipes by making it so that we Amass whenever a Sliver dies, but it also gives Slivers we control Afflict 2 which disincentivizes our opponents from blocking
These are all fine and playable in dragon Commander decks, but you can do a lot better with other commanders, even dragon commanders
Its powerful enough that I could see it in a ramp deck of some kind, so its not useless, but its not all that special
Furthermore, there are many more widely played formats (such as Tiny Leaders) I could provide a link to, but the reality is that if you include all those formats in your definition of previously banned, some person will eventually just invent a format that bans every card but basic lands, and therefore will be able to tutor all cards
Big Mother Mouser | 4 Colorless Mana Artifact Creature Robot This creature enters with two +1/+1 counters on it
Coat of Arms, Obelisk of Urd and Harsh Mercy seem to be the best rewards for plaing Full tribal