St. Pattack is a platform fighter with just a little bit of charm, where you get to kick the ever living tar out of a bunch of leprechauns.
There are two difficulties, easy and hard. The differences are that on hard the enemies have more hit points, Pattack has fewer, and bowls of stew don't seem to drop as often. You also must be playing on hard in order to get the last two medals. It also takes more coins to advance to the bosses in hard mode.
In order to have any chance at all of surviving, your best bet is to take the high ground. This will minimize how many leprechauns you have to deal with at any given time, and it will let you knock them down, to minimize the damage they can do to you. Note that they like jumping up behind you more than jumping up in front of you, so plan your gameplay strategy as such. There's also no really compelling reason to not always be attacking, unless you're going after the don't hurt sheep medal.
You can block and do your dash attack in midair, which can be useful at times. Before you encounter the final boss you'll lose all your rainbow attacks, so you may as well use them all up on level 2.
There are 3 main enemies, plus the two bosses, plus sheep.
They can't fight back, and they make a satisfying thump when you hit them.
They slither around, and they can hit you, but only if you're standing still. Otherwise they'll just follow you around.
Leprechauns like to fight. These are the first type of leprechaun you'll encounter in the game, and they'll walk up and try to punch you in the balls.
These leprechauns toss their clovers at you from a distance, and are more dangerous than the boxers because of the added range they bring.
He commands the elements, except for fire. And except for rainbows, which you can fire at him rather than the other way around. You need to hit him with rainbows and his own boulders, by deflecting them back at him, and then get out of the way so you can trade positions with him.
The final boss. First you beat him up like any other leprechaun (though slightly larger), and then he grows to Hyde proportions everywhere above the waist and comes at you again. To defeat him, use the platforms to jump over him, and hide under the platforms when he starts dropping bricks, in order to avoid getting hit. Once he drops them he gets hit himself, and he will be dazed until you hit him to knock him out of it.
(note: second video has just been uploaded to YouTube, and may not yet be ready for playing; be patient)
After defeating the Druid, you'll get to play the bonus round, in which you hurt sheep and collect the stew which is made from them. The more you get here, the more advantages you get when you return to the game. Anything that shows up in the achievement list gets added to your character, so if you get the potato and 3 cups of ale (my personal best) then you are slightly healed and have full rainbow power again.
Juggle some leprechauns a lot. It's unclear exactly what the juggle requirement is, but odds are you'll get this playing through hard your first time on hard. It can also be attained in easy mode, but it takes a bit more luck to get a leprechaun who won't die too quickly.
Play the game on St. Patrick's Day. Or, if you missed the special day, you can change your computer's clock to March 17 and you should get it anyway.
Finish the entire game without hitting a single sheep. This can be attained in easy mode.
Finish off all of level 1 including the Druid without losing a life. This must be done on hard mode.
Beat the game on hard mode.