Forsaken monument and sun are exactly the kind of payoff cards that you should be looking for - stuff that cares about your creatures, draws cards and makes more mana.

Myr propogator is a weird one - I've run cloning effects with Followed Footsteps and Cogwork Assembler type effects, which can be strong, but they mostly need something else to make them great.

Propagator is a little slower than them due to the tap + cost, but also a little more resilient due to both myr having the tap effects. If you were shooting for a Myr Galvanizer combo deck propagator will works as a payoff, with a backup where you were sacrificing tokens to trade for cards on a stalled boardstate, or perhaps were generating tons of mana with a myr Priest of Titania (if they print more myr support) it might be great, but it just needs a lot of other cards to work - haste for the tap cost, 3 mana for the price, ands its still a 1/1.

Short of shenaigans with something like Dollhouse of Horrors Necrotic Ooze or Mindlink Mech, I'm not a fan. It just takes a lot of cards to make paying 3 mana for a 1/1 artifact token to be good.

I feel like its just a question of finding the cards to bind the two strategies together - bigger spells that like you having myr in deck/hand, and smaller myr that like the big cards you cast. Myr tribal is going to rely on card synergy to keep up with other lists.

For the smallest possible change, I'd look at Icon of Ancestry - it can help your myr trade more effectively, and find cards when you start running out of steam. Things with effects you can sink excess mana into will work well here.

Before that thouhg, playtest hard before going out to get cards - it saves a lot of stuff ending up stuck in the trade binder, especially when brewing this kind of list. It'll take a bunch of false starts before things start feeling right - if your deck feels best as Shimmer Myr flash artifact control, then investing in aggro tribal tools might not be ideal.

I like this idea, but I feel like it needs some draw power and big payoffs - a couple playtests and I was sitting on lands and myr without a big 'this is how I win the game'.

I think the biggest thing would be leaning into green for Winding Way. It would let you grab myrs for the myr gameplan or grab tronlands in the top cards of your library, as well as opening up Ancient Stirrings which finds every card in your deck.

Icon of Ancestry / Brass Herald offers this kind of effect at a higher cmc but colourless.

The difference between 'big mana' tron myr rather than more 'artifacts cost less' myr is that it changes combo options - Myr Retriever loops and Heartless Summoning isn't going to do well. You need some big artifacts that stick and turn your myr into big threats - the myr tribal artifacts only do sorta okay at this, but they're a little light on synergy with each other.

If you want big winning combos, its more likely to be Kuldotha Forgemaster type cards that grab a big artifact threat - most of which would be lore appropriate.

I've had fun with Trading Post in these lists, alongside Myr Sire/Genesis Chamber to create a 'value until your opponent runs out of cards' style, but it does need the myr to be able to trade efficiently.

Trying to stick something like Vanquisher's Banner then play your entire deck, or run things like Thoughtcast, Lead the Stampede or Thought Monitor (with the artifact taplands) are all neat options but would take a lot bigger changes. A slow list built around using myr as mana dorks, artifact lands and Storage Matrix has some potential too, but all these options are getting further away from what the list currently is.

Have fun, and good luck with the playtesting.

I'll echo other commenters - focus in on lands and staples. A deck with bad spells and good lands usually outperforms a deck with bad lands and good spells.

Arguel's Blood Fast  ^Flip, Eye of Vecna Dreadhorde Invasion, are all worth playtesting to see if you can support a slower gameplan, cause getting life low without fetch into shock is hard.

I'd go mine death's shadow sideboards for cheap tech for whatever matchups you feel weakest against then run it mainboard. Unholy Heat & Terminate are worth looking at for spots if you can support the mana pips.