Thanks for all the hints
So unstable hourglass deals 13 damage per card in every other turn, this translates to 6.5 damage per turn per card,
and the current upkeep cost is 4
for playing card + 1
for activation for every two turns
so the average upkeep cost per turn is 5/2 = 2.5
To sum up, total cost for 6.5 damage per turn is 2.5
+ 1 card, much cheaper than Titan.
In order to balance the card, the damage per turn should be reduced to 3.5 so the damage caused by each activation/destruction of unstable hourglass should be 7
Is this correct ?
But still, will this be underpower ? keep using UH means you can't get new cards but Titan won't cause this trouble