What's the main game plan of the deck, if you had to summarize it in 3 sentences or less? Cause I'm seeing a handful of half-ideas that are likely to result in some games where everything comes together, and other games where you end up with the halves of 3 different win conditions without closing any of them out.

One example of this being Aetheric Amplifier and Doubling Season. Only about 6 other cards in the deck seem to interact with counters. And while Doubling Season also doubles the tokens you get from Riku, you could run Parallel Lives which has the potential to curve better into Riku.

A general rule I follow, is that any synergy piece (Or card that doesn't do anything without something else to activate/trigger/synergize-with it) MUST work with AT LEAST ~25 other cards in the deck. Otherwise, in about 2/3 of games, it's just going to be a dead card. If it works with the commander I can let that number be a little lower if it's really strong. But an important part of any deck is to think about how it works if the commander gets permanently/repeated removed, stolen, or Frogify'd.

Another important thing about Riku is, they take a lot of mana to function. In order to use their ability, every spell you want to copy essentially costs 2 more. So look at which targets you're planning to copy and consider how much mana you're really gonna need to pull off your plan.

An average deck template suggests about 10 pieces of ramp. Your deck currently has about 7, and a lot of them cost more than 2-3 mana. So you're already running less ramp, that ramp is fairly costly, and you have a very mana-hungry commander.

Your mana curve is really heavy in 4-5 cost spells, and that's a tough place to be if you ever want to cast more than 1 spell a turn. Even more so if you want to copy anything with Riku.

And just in case you don't know, I don't think you can copy Apocalypse Hydra with Riku. Or, you can, but the token will enter with 0 counters on it and die immediately. If that wasn't you plan, then ignore this, but either way, I'd suggest removing Apocalypse Hydra and Atarka, World Render. With no other dragons in the deck, Atarka is just a big trampler and you're better off using a cheaper one that you can actually make copies of.

I hope this was helpful!

If a creature does damage when it enters, is that too late for Gev, Scaled Scorch's first ability to put counters on it?

I'm building a commander deck with Gev as the commander and I was wondering if Impact Tremors would allow creatures to enter with counters from Gev's first ability.

The way I'm reading it, would suggest that the damage happens too late, but I just wanted to be sure and couldn't find a solid answer elsewhere.