hmm...
upgrade ice shield after you've upgraded all towers
it add +1
to the cost but -2 damage reduction, most FGs will have swarm with 2+ damage critters, you WILL want to have permafrost (deck's MVP)
the 2nd pulvy and the 3rd hourglass take priority over everything else because their ability cost reduction is critical
2 hourglasses are more than enough in a 34-card deck imo (i'd suggest either protect artifact or jade shield in its place)
quint and antimatter fall between those above and below
as for fire queen, my variant ditch it completely but if you're keeping her, remember that golems are not entirely reliant on fire queen but elite queen produce 4|2
generating fireflies so you can either upgrade it asap or upgrade it later
last to upgrade: lava golems, fractal
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the variant i'm using also ditch miracle for heal instead, +20HP is nothing to scoff at...sure MAX-1HP is better but the difference between 12/15
to 2/3
is huge
edit: i disagree with the poster above about fire queen (FQ) priority because my own testing shows that FQ is the weakest link in the deck but it always helps to have 1 Elite Queen which can be use in other rainbow
though i think you might want to hold on upgrading FQ because as you fight FGs, you will win it from the spin eventually