I feel, that the name Shard of Focus does not fit to the card. Focus sounds more offensive but the power looks like a gravity effect. Therefore Shard of Gravity would fit better to this card.
The original version of the card is like a three to four time useable pulverizer but the issue is that first the power is useable for free and second it buffs the shard.
Second is that gravity would not get an additional benefit as like in the other shards.
And I'm thinking about a different version of this card:
Version 1
Shard of Gravity (creaturelike style)
It starts as a 2/10 card
The power accretion works now this way: Sacrifice a permanent and gain +2/+10. It will becomes a Black Hole if HP>40 (50 if your mark is
)
Now you need to use your own permanents to fuel this shard and gravity get an additional bonus. Overbuffing it (ex: using a Blessing on it while being at 8/40 (10/50 with
mark) will turn it into the BH.
Version 2
Shard of Gravity (permanent style)
It starts as a permanent with no counters
Power accretion works here this way: Destroy a target permanent and put a counter on the Shard of Gravity.
If the number of of counters is equal or more than 2 (3 if the mark is
) it will turns into the BH and the owner of the shard will receive 5 damage per counter from the implosion.