Let's look at the running guy first:
- Make sure that his feet are not sliding. For instance on the first step at x205, flip back and forth between 205 to 210 and you'll see how the foot slides forward and then back again. The same happens during the next step. You will have to either adjust your cycle or go in there frame by frame and make sure that the feet are locked on the ground.
- Continue with the breakdowns for the rest of the run
- I would tone down the head turn as he looks to the cards to the ground a tiny bit and the same goes with the reaction. Watching it now it feels like he's super surprised and excited that he found the card. Shouldn't he know that the card is there? I think that section is a bit over the top.
- once he puts the last cards on top you could vary the timing a bit in his arms, they look a bit floaty as they go up
- the fingers during the last positioning of the cards are a bit crude, I think you could have more delicate poses, for instance holding the cards with two fingers only, or something a bit more in the direction that he's very concentrated and precise with that last move.
- watch your eyeline when he puts the last cards together; looks like he's looking above the cards away into the distance; lower the eyes a bit
- the head turn at the end feels a bit soft and it looks like he's looking ahead of the guy running at the end
- the kid's reaction feels a bit simple after the guy runs by. He looks at the runner, then at the cards and when the cards fall his reaction doesn't really change that much. I would push that section more so we can see a bit more thought behind it. He could look back at the cards in fear, then relax because the cards didn't fall down, but then they fall down and he's really shocked and then closes his eyes in anger and frustration, something like that; I think the current disappointed body slump is not enough of a reaction
I'd work on these beats first. Keep going!