September 2018
When playing pvp for event tickets I have noticed that if you play a plant hero, only Grass Knuckles or Nightcap will ever earn you the most tickets. With zombie heroes it varies a bit, but with the plants it's always these two and I am getting pretty fed up playing them.
Also, about a year ago I would occasionally see 750 gem packs for Beta-Carrotina and Huge-Giganticus (my only missing heroes), but no more. It seems both are suddenly unavailable.
September 2018
You just have to wait, when they come available again. I'm sure it will happen occasionally.
November 2018
The same thing happens to me. The only plant heroes that ever get the 10 times ticket boost are Green Shadow and Beta Carrotina. It cycles through all the zombie heroes but not plants.
November 2018
I'm sorry to say that this is a bug that has more than a year in the game, It has been mentioned many times here and we also reported it by mail hundreds of times.
See this post:
https://answers.ea.com/t5/Technical-Issues/10x-Heroe-always-the-same/td-p/6674598
it's not going to be fixed, since this game is abandoned in every way, and neither EA nor PopCap take care about this game in the least
November 2018
Almost 9 months later, I'm quite disappointed in these two companies, and there is no doubt about not being, I understand you guys, how annoying it must be to collect tickets with the same heroes, but there is not much more that can be done.