I just beat the first boss on hard mode difficult and thought I'd share what worked for me since so many people are struggling. I used the pixie pet and had all points in trapper.
To begin, construct a freeze trap on the first crossroads adjacent to the enemy spawn location. Next, build a mist tower on the north side of the crossroads. This one tower kills all the snakes about 75% of the time without breaking your trap. Collect the money/gems and build a stone tower on the southern side of the crossroads. Build freeze traps all along the open stretch (I built 5 before the boss spawned and another while he was in the second freeze trap). As soon as the boss gets out of range of your towers, sell them and run to the second crossroads by your crystal and build 3 spear towers on whichever corner the boss is coming from. You should have enough mana to build another freeze trap in this area. Regardless of how much gold or gems the enemies dropped, this strategy worked for me 3 times in a row, no gems necessary. If the boss walks northward, the mist tower will get an additional slew of shots and this strategy should work even better; however, I found that this is not a necessity.
If you chose the pixie pet, don't spawn waves early. If you do, you will not receive mana during the off time. If you do this correctly, you should be able to freeze the boss 7 times. Make sure you never have a full mana pool; if your pet's bonus kicks in and you have full mana, it was wasted.
If you did not chose the pixie pet, this strategy will not work on hard mode (it may on normal--for sure does on easy). You may want to consider restarting to get the pixie as it has the best special by far. If you chose the Loomi, you will have a very difficult time unless you are on easy.
After beating the game on normal with 3 stars on every level, this level is by far the most difficult considering how few points you have to spend. If you clear this level, the rest of the game is smooth sailing. If you cannot get this strategy to work, let me know and I'll try to help. If you are trying on hard mode, it may take a few tries to get the timing down.
Some corrections to your post: "This one tower kills all the snakes about 75% of the time without breaking your trap" Out of 75 attempts, the mist tower killed all snakes 3 times.
If that's the case, you're doing it wrong. Regardless, it is still doable if you have one less trap and few less coins--especially if you get a gem. I've tested this strategy more than 20 times in HARD mode and have found success in nearly every attempt regardless of whether it killed all the snakes.
I've found that the mist tower kills all the snakes more often if it is on the north side; this may be your problem. It should also be on the outside of the square made by the paths.
As a side note, if you get a freeze gem from the snakes, place all of your traps on top of each other at the crossroads. Your freeze-gem-mist-tower will freeze the boss two to three times before even getting to the trap and should die before he breaks all your traps.
I just saw one of your posts mentioning different results in different browsers. I was not aware of this, and this was likely why your were struggling with the snakes. I played in Mozilla Firefox.
This strategy worked wonders for me, even though I failed pretty badly on the execution and only got four freezes at the first crossroads and one on the second. (I got a shock gem for the mist tower, though.)
As another obvious milli-tip, if all you have mana for is a poison trap and the boss is closing in on the gem, fire it off. I'm pretty sure that was the finishing stroke for me.
