This one is very simple. Just go to the credits and put your mouse on the bumblebee logo. A portrait will appear and you'll get the achievement.

1- One may be tempted by the idea of using certain towers because of the fear of certain enemy units (like using fire against minotaurs or arrows against harpies), but that's useless on hard mode. Gargoyles and magictowers will be your best friends, and use only them for defense. The stages where these two aren't unlocked yet are pretty easy, so you can easily win using only arrows and miniguns.

2- Don't spam units like a NPC. The only time you'll ALWAYS want to spam units is in the beginning of each stage, but only one or two waves of units will work. If you try to spam units on mid or late game, there's a chance to occur a very saddening phenomenon that i call enemy blob.
When spamming on mid or late game, your units will fight against buffed enemy units, that will have to stop for the sake of fighting, and sometimes all enemy units will merge into a single blob and won't split ever again, and so they'll instakill all your units and towers.
"But that's inevitable", you may think, and yes, you're correct, there will be a time where you'll have to fight against an enemy horde, but you may pick the right time to do it. And the right time is: when the dragon spell is ready. Use it the closest possible to the enemy barrack and spam your strongest units (like minotaurs, trolls and centaurs). The stages where the dragon spell aren't unlocked can be beaten just using fireballs and cyclones on the blob.

3- Don't spam towers as well. It's better to have two or three full upgraded towers than a lot of basic ones.

Skilltree: Your first upgrade should be the chicken production one. After that, upgrade all your unit status in this order: all damage upgrades, all movespeed upgrades, and lastly the health upgrades. I don't recommend focusing on towers upgrades, since you can easily beat the game without any of them, so you may upgrade your gold production and skill cooldown after upgrading all your units.

Characters: The best character will always be Ariella (the harpy queen). Her special ability is useful for destroying enemy towers without even having to touch them with your units (remember that fireball damages towers too). You can also use the cyclone to damage enemy units, but BE AWARE that it damage your units and towers too. Eventually you'll have to play as Violetta, and the best combo is using her charm ability when enemy minotaurs are close to enemy towers, if lucky, you'll get them, and use the ice spell on the aimed tower, sometimes you can take it down just using enemy units.

The GMG: My favorite defense style is 2 gargoyles with 1 magic tower in the middle, that i call GMG (gargoyle + magic tower + gargoyle) style. Sometimes you'll be able to put 3 gargoyles around the magic tower, and even totally surround it with gargoyles!Try to get a tier 3 gargoyle as soon as possible (don't try to put just one gargoyle and upgrading it, it won't work), and upgrade the others afterwards as you wish.

The blue color means gargoyles, and the red color means magic tower. Build your defenses like this in these two locations:

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Don't use minotaurs in the beginning, because they take too much damage to poison, and you'll have to fight against spiders and spiderriders. Use trolls and centaurs to destroy the barrack in the far-left of the map.

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After this, go straight to Cinda through the mid lane using minotaurs and centaurs, and go for Letchett afterwards. You have to win as soon as possible in this part, so the barrack in the far-right of the map doesn't get too buffed, so remember to use your spells.

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This level is quite simple and sometimes, luck based. When the stage begins, instantly destroy the cheertower on the left, and build your GMG defense like this:

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• Attack the far-right barrack using minotaurs as fast as you can (and don't forget to upgrade your gargoyles on the left). Then, just be patient and try to win through the mid lane (of course). Spam bloodrain and trust in your dragon spell!

This is a guide, not a holy book. If you're having other problems in beating the game using my tips, you're free to ignore some of them or even improve them. Be flexible and creative.