got inspired by that fun build:

http://www.ultimate-bravery.com/ub.php?data=aJ64081lDiW4JUejpR4prIwLa0UDhKebOgRvpwyq6ar9oSnQ0yEixjC4rVpiphYyxLAzN8WultV_eLTlX9PuYg

had a funny game with it, but dont know how viable it is.

You have a big power spike after getting frozen mallet, you can gapclose with your q control the distance pull/push em with your e, non-stop slow the enemy champions with your basic attacks and when you want to escape or keep em close till your teammates come, and most likely slow em till your q is up a second time.

you are reasonable tanky depending on your runes/masteries and still do lots of damage with your abilities and your basic attacks. it feels a bit like you are a spider and the enemy champions are flys, if they get to close they dont get out of your net, much slows and other cc its nearly impossible for them to disengage with most champs, the only way for them to get away is that you disengage from them or they kill you :)

Still you are support and it takes you a while to get that base items and if your team ****s up completly or they have some/much hard cc its far from op but it gives you much outplay potential and good teamfight followup potential

with that build you can make people pay for mistakes. but I guess there are builds that are more forgiving for own mistakes and have a earlier power spike.

Of course you can squeese in a wardstone as one of the earlier items, but it delays your power spike further.

Its maybe not the best build for thresh, but it fits a different playstyle :)