Yeah I really don't see Teemo getting any benefit from the higher Tiers of any of the trees. I totally agree with your masteries, should replace the MR in the defense tree with some utility. But it doesn't matter now, seeing as they're completely re-vamping the masteries :3

About the color and boring(ness?), I wasn't aiming for people to read this, I was really just putting my thoughts out in writing.

As for the Frozen Mallet, I really enjoy the slow it applies, since I can't always have the luxury of Red buff, in case a melee character might want it more, and Teemo is inherently squishy as hell, so he really benefits from the extra health. And the 20 AD...well more damage isn't a bad thing. Though I wonder, just for the sake of wondering, does Teemo's toxic shot damage proc Rylai's?

Guardian Angel: You're totally right lol but it's an item I usually get just for the balance of Magic Resist and Armor. Any other survivability item is totally viable, as long as it caters to the enemy team's composition. I listed GA because more often than not, I get it. Though a Banshee's would be really useful, since Teemo's attack range is relatively short, making him vulnerable to CC.

And Black Cleaver...It's really personal choice at this point, a Void Staff to help with the On-hit proc items (magic damage), or another survivability, or maybe a Wit's End, or even a Nashor's Tooth. But I like the Black Cleaver because in addition to more damage and attack speed, it shreds armor and I feel like the damage gained from Madreds, Frozen Mallet, plus base damage (around 150 AD) is wasted to no armor pen. It's sort of an OCD thing for me, I'm like AHHH MADREDS AND FMALLET DOES AD AND I DON'T HAVE ANY ARMOR PEN I NEED TO GET ARMOR PEN OTHERWISE I TOTALLY WASTE TAHT AD. Or something like that lol. Yeah I know, not a good reason :P probably better off going with a Wit's End for the MR and 42 magic damage proc plus AS.

''I feel like Teemo doesn't benefit from specializing in one tree. Therefore, I spread out his points in different trees, getting what is useful for him. I don't think every point needs explaining.'' I feel you on this. This is what I use on teemo and other similare champ:

1: More Image and color so borring to read.

2: Frozen mallet???? really ? you can't pick something so unusual without explaining your self.

3: Normaly Guardian Angel is a optional item on carry since if the game goes well you should get something else­.

4: Your build seems to focus on magic proc dmg so why buy Black Cleaver?