Bosston?
are you asking if any card, including 2 star cards can One Hit?
or are you just saying that even when you use One Hit cards like
Kinjo, and
Lost Hog, you fail to get the killing blow?
if the first?
then you need to meet the requirements, as in have a card either with 8 damage + 2 damage bonus, + Fury.
or card with 4 damage + 6 damage ability, + Fury
or in rare cases, cards with 7 damage + 2 damage ability, or bonus, + Fury, and
Timber
if the second, it is probably because you have bad luck with random.
if you play 9 pillz + fury, there is a chance your opponent will either block with a damage reducer, block using 6 pillz(and let random do the rest) or use more than 6 pillz(which in my opinion is wasteful, and still won't guarantee a sure shot).
there are other options, but i figure these are most common.