Just keep on chomping on them delicious muffins.50 for Pile o Muffins and 100 for Cart o Muffins. These are not all the possible muffins you can find in the game (there are actually 201) so you should be able to get the achievements relativelly easy through the story.

Kill 30 and 100 heroes, respectively. Again, these are not all the heroes in the game; there's 195 of them. Some tips:

• The game provide means to kill them on several ocasions, like barrils to drop on their heads, rocks to trample them over. Look out for those.
  
• Hang on the wall right beneath them, almost on the edge and they will walk on your head and fall.
  
• Use and abuse bomb dispensers (although not all heroes can be killed by those).

Die 500 times. Easiest achievement EVER (for me at least).

On level 05 The Boss of Rage Quit, you have to get one the boulders to the breakable plataform and push it till you can jump over it. Follow the path and you'll trigger a cutscene with the paladin.

There's actually two places where you can find the swamp king. At level 01 Down The Well and 05 The Boss of Rage Quit. In the first, when you get to the part where you lit 3 barrels on fire to explode a wall, grab one of them and take it to the breakable wall near the area with 4 imps. Explode the walls and you'll find the king. At level 5, when you find the door, jump left and climb the wall. If one of the door there isn't open just backtrack to the begin of the level and go there again.

You'll need to ride Sarah (no pun intended) to complete level 11 Do you Even Lift, so it's a easy one. Jump on her back before or right after she tries to smack you into a pancake, then start moving. Careful not to move when she smacks the warriors or you'll fall (and probably die).

On level 13 Save the Duck, to ride the sheep just jump on it, like you did with the troll. You'll find it on the hole right before the level exit.

On level 08 World Tree, after pulling every levers possible, right before jumping to the woods go back to where Groenk was, the door will be open.

In level 13 Save the Duck, after you open the hatch with the ducks, sink into the water and go into that hatch, then onto the portal right after, then in the portal in front of that portal. Or you can, right before the end of the level, roll the bolder into the breakable platforms, go down, pull the lever in the thief room then go into portals.

You'll automatically get this when you reach level 14 on the road.

This guy is so f-ing annoying. And hard to kill. Hate him.
At level 08 World Tree, stay the closest you can to him so that he gets hit by the fireballs the mage will be trowing at you.

You can't just pick any knife dropped by some warrior; it must be your own. The first level you find the goblin knife (after the tutorial) is 10 Backstabber. It has a red jewel to differentiate it from common knives. Don't try to kill anything other then mages, witches and shamans. You won't damage warriors even if you hit them.

Pick up and trow 15 different skulls. I recomend level 2 or 3 since they're at the begining of the game. Just have to go to the trouble of opening the secret areas.

Die on spikes 25 times. Super easy. Just find some near a toten and jump on them repeatedly.

Another easy one. On level 12 Boss of Feathers, when the cutscene ends, wait a little, get transformed into a chicken and jump on the spikes. Or don't, there are so many other ways to die, choose whatever you like.

Find a explosive barrel dispenser and light 20 on fire. First level with this kind of dispenser is 08 World Tree (not counting the tutorial).

"I just found The Motherload. It's in Level 11 "Do You Even Lift?". To get it, you need to climb on top of the fourth building and activate the lever. A platform will descend, taking you to an area in the sky with a jumping puzzle. At the end of that, you will find the Motherload. " by user Spezializzt.
Thanks a lot for sharing this.

This one is pretty self-explanatory. Kill the paladin. But watch out that you can't harm him until the very last level. To be honest I haven't beaten him yet myself.