In the past we had a lot of small events using the event tracker. That system was really cool even if some people abused a few events.
So I think there should be care about what to choose as rewards. I list a few of my ideas down below. Bad rewards (Don't give it as reward because people would abuse it)
Joker Box
G1C
Good rewards (Nobody take a big advantages and cannot abuse that event using other accounts)
Gear Selector
Weapon Skin Selector
(10 Days) Weapon Selector
Clothing Item
100-200 Joker Tickets
Title
Event examples
3 Blow Torch Kills - 200 Joker Tickets
20 Sniper Kills, 10 Pistol Kills, 2 Grenade Kills - Gear Selector
10 Pistol Kill in a row (Killing with other weapons interrupt the progress) - Title