so just went in to beat stage 1 again.
heres a tutorial.
send anyone down any lane for the first round, it doesnt matter, the whole point is the first round gives you a ton of xp regardless. dump all of this xp into the green slingshot guy, on the range stat in the middle.
this should give enough range to attack the golden pot on the middle lane without being attacked by anything, this gives about 30 xp a round.
use this on range, getting 3 units max, and damage on the green guy if you dont have enough for range. you dont need much damage, 4 or 5 is enough, you dont need rate at all.
range 8 or 9 should be enough to start clearing the majority of the board with just these three units. 10 definitely clears it.
it will clear it, but one or two units dies, at this point upgrade your max units to 5 or 6 so you can send in more guys once the board is clear. they will have a free run to the ropes.
should win by run 12 or 13.
and if you pay attention to your enemies, the flower in the middle lane seems to be the best ranged unit they have, this is your unit of choice in the next stage to upgrade.