League-of-legends – Error getting free alistar and free tristana

Apparently the redemption page doesn't work properly in some browsers. I had the same issue and had to ultimately use Internet Explorer (rather than Chrome) to get Tristana.

Don't worry too much about trying to get kills - Alistar's role in a match is to provide support and disruption. You may not get many killing blows, but if you're a decent player, you should have many many assists instead.

If you're worried about losing out on the money that comes with kills, I'd suggest you look into Gold/10 items on Alistar - Philosopher's Stone and Heart of Gold being the better of the 4 for him. (Duplicate items don't stack, but there's nothing stopping you from picking up one of each).

That said, Alistar makes good use of Sheen, which is a cheap way to double your basic attack damage, and gives him mana to boot.