Multiple-double damage
While I was fighting versus a player, he was using two "Calamity Bearer" giants, which have the ability of double the damage you or your creatures are going to inflict to an other player or to his creatures.
When there were two "Calamity Bearer" the damage I got was ×4 (is applicated one ability and next the other over the first, bht these abilities were called together, so right is get normal damage ×3:
basic damage + the same basic damage by first ability + the same basic damage by second ability=
=basic damage(1+x), x=number of doubling damage.
Ex.:
Two Calamity Bearer 3/4 controlled by player 1, a giant attacks player two, player two gets ((3)2)2=12 points of damage, but the abilities of the two giants have been called togheter, so x=2, so final damage=3(1+2)=9.
Similar problem with "Vorinclex, Monstrous Raider", a card I use that has:
"If you would put one or more counters on a permanent or player, put twice that many of each of those kinds of counters on that permanent or player instead.
If an opponent would put one or more counters on a permanent or player, they put half that many of each of those kinds of counters on that permanent or player instead, rounded down."
For this i suggest the formula
New damage/counters=z*(1+x)/(1+y)
Z=basic damage/counters
X=doubling abilities
Y=halve abilities
It can not be all correct but this is my suggestion, I don't work at this game and I see only beautifull cards, not wath is over.