RisenDeep

Why not use Eldrazi Displacer instead of adding so much one.time trigger cards like Cloudshift and Ephemerate?

Heartless Summoning is a nice card but you don't even scrapped it's potential. Ever wanted to have a Dark Ritual for red so play Priest of Urabrask to get 3 Red Mana and also a free Morbid Trigger or use the Grinning Ignus mana generator to get your dragons out more fast. Maybe this is a good option for Dragonstorm

Looks ok, maybe some fewer lands and add some Tarfire

If playing for budget you should consider playing Siren Stormtamer as replacement for Cursecatcher,
Pyramid of the Pantheon to replace Aether Vial (not exactly but it produces a lot of mana once fully charged)
and focus on Merrow Reejerey and Stonybrook Banneret to potential one-shot your entire hand to the board

I see a problem in board removal, killing your servants (Myr, Goblin, Shaman) will prevent you from playing the big guys early so maybe you could consider adding some Planeswalker to your deck for a little more support.

Koth of the Hammer for example can produce a huge ammount of mana but isn't cheap to play with CMC 4 while Sarkhan, Fireblood seems a better option and you aren't stuck at mono red dragon spells anymore.

If you want to splash, Domri, Anarch of Bolas is a good option not just for the additional mana but also the power boost it offers and you'll also get an option for removal (having your dragons fight anything).

What I like to play is Dragon Arc and fokus on multicolored dragons and something like Captain Sissay to fetch anything I like

I didn't read that "or both" text so yeah in this case, your card would be a better choice. I think it will anyways depend on the meta you play your deck at, against tempo removal Regrowth could be CMC 2 a better option while Esper might the other one work better

You might consider using Regrowth instead of Fortuitous Find for a better mana curve and you can regrowth anything if needed

I just felt like it!

Mox Amber triggers in turn 3 after I put one of the walkers out to the board and due to the legendary rule, I'm able to drain up to 3 extra mana then for playing something else. (Play Mox -> Add Mana -> Play Mox -> Sacrifice the tapped one) It is always worth to have some more mana in a control deck so yes, I feel like having a possibly dead card on the board seems like a good idea if I get some extra cash in the back hand. Also it isn't about "just playing something for 5" rather than possibly have mana left in the wide range to cast some extra spells if needed.

Etrata is a card I like for the first point and also a card that can possibly make some preasure because it is unblockable and with power 3 a good hitter. IThe 5 defense make it hard to get her away from the board unless you make a 2-for-1 change in most decks. Also she gets rid of some creatures if there are any so she is a reusable removal spell and also legendary so it is possible to have Mobilized District become a creature for free

Ok, good idea

Is Urborg fitting into the Commander color rules?

You are missing one card for the 50 cards limit and why do you play Urborg?

As of official Wizards Website, Deathrite is still on the Banned List of Legacy Format

You could make this a realy realy ugly deck when you use the full power of Lorwyn ;)
Foundation:
Thistledown Liege and Wizened Cenn each increase the power of your Kithkin army when they're on the board. The masses get stronger but you will need the masses first.

Militia's Pride and Patrol Signaler each recrutes more Kithkin as they they are in play. You could combo Patrol Signaler with Springleaf Drum, one of the most underrated cards in the Lorwyn Block.

Kithkin Harbinger ensures that you draw the needed cards and can also seek for Tribal Cards like Militia's Pride

Extras:
Knight of Meadowgrain is a good card to negate early game mistakes with it's Lifelink ability.

Kinsbaile Borderguard as you already play it, is just usefull when it dies to bring more Kithkin into play but a late game drop to boost it's ability best.

A two drop Ajani Goldmane will power your deck additionally with it's -1 Trigger.

Back Safety:
Order of Whiteclay to return your Kithkin from the graveyard back to the board. YOu can trigger it instant by also using Springleaf Drum on it.

Maybe:
Crusade to power your Kithkin even more, but it is an Enchantment so it put it onto the maybe list

The idea is nice but I think you are too slow for a regular Goblin deck until you get Mirror March onto the table

With an avarage of 18$ per piece I don't think so

Going budget you could also think about Glintsleeve Siphoner and some Energy improvement like Aether Hub or Gonti's Machinations to ensure a filled hand at every time

Adding Springleaf Drum is a good option to trigger the Tap triggers of your Merfolks and to obtain additional mana. Grimoire Thief together with Harpoon Sniper are very good control expansions.

I played such a Deck in Lorwyn standard

I can recommend Nissa, Steward of Elements and Deeproot Elite/Metallic Mimic as same as Merrow Commerce. Thada Adel, Aquisitor is a better Rootwater Thief in my opinion

I'm playing this one
https://www.mtgvault.com/risendeep/decks/merfolk-26/

for a couple of months now and it seems to fit the meta

I think Biomancer isn't worth taking the Cursecatcher slot for a couple of reasons. You have Silvergill Adept as an instant card draw, Biomancer needs to pay an extra cost and/or put a counter on it. This are two factors that can be interrupted by an opponent and so prevent drawing cards for you. Biomancer dosen't generate a card advantage because it says "then discard a card" so it is worthless to refresh your hand with a couple of new cards. Last but not least Cursecatcher has a more generic advantage of countering spells that may make the difference in the game, early as same as in late game.

Biomancer is a usefull card in decks where it's ability could be triggered more frequent like when playing along Sage of Fables or a green splash and a +1/+1 counter focus using Deeproot Elite and Kumena. It may also has a slot in decks where cycling through your deck is an option to find something unique