2 Suggestions and 1 Praise for Nexus Blitz
Suggestion 1. The snowball fight event seems really out of place. All the other events force champs to group around a specific area and promote the hectic teamfighting the whole gamemode is made for. This doesn't do that at all.
Suggestion 2. The On Fire buff is interesting, and it's really fun when you have it and you can just roll over the enemy team, but, the increased damage output in return for increased damage taken is not something you want on every champ. Particularly when you want to be the tank and happen to get the buff, it's exactly the opposite of what you want. To a slightly lesser extent, if I pick a bruiser or fighter champ, having my somewhat balanced mix of tankiness and damage being skewed so far to the damage side doesn't feel great, though I can understand where people might disagree more on this second one. I don't know how feasible this would be, but If I could change it, I would make the buff give super adaptive stats. Giving you a certain amount of armor/mr/health/ad/ap/attack speed based on what you're building, though the On Fire effect would probably also have to be nerfed in some way if this change really happened.
Now, my praise. I have to say I think Riot did a pretty good job with the events overall. Although Bardle Royale, King of the Hill, Scuttle Crab Racing, Push the Cart, and Loot the Teemo all push both teams to do the same thing, they all have their own defining features. Even though you always end up teamfighting when one of the events occurs, since each team's strategy will be slightly different based on what each event demands each fight feels unique and interesting instead of repetitive. It's also fun to see your champion have some special interaction or great synergy with one of the events.
That's it from me. Hope you enjoy your next game of Nexus Blitz.