How to get him as a challenger: Get Sneezles or Neoflu then go to your pet's quick reference page here
Difficulty : 60
Starting HP: 75
HP gain per win: 7
Weapon you steal: Downsize Power Plus
Avatar for beating him:
1. Spin the Wheel of Excitement, you might get the diesease from there.
2. Spin the Wheel of Misfortune, it can give you the diesease.
3. Feed your pet snot burgers, some people have gotten the diesease that way but this method does not work for everyone.
4. Feed your pet rotten omelettes, it can give you pet a random diesease.
For for the part on beating him. Well first your pet must be of a high hp, it doesnt need to be too high but at least of a reasonable value, since his Meukas Snot Trail and Radioactive Muffin can do more then 60 damage a single shot (killing your pet instantly if it has lesser then 60hp:S) Well to beat him, unless you are willing to buy real expensive (at least 300k) weapons to beat him, you will need to spend some nps buying one use weapons. I recomend sticky snowballs, evil muffins, battle muffins,Silver 00 Hog Battlecard, Silver Fernypoo Battlecard... well there are quite a lot of them u can use... go take a look at my recommended one use weapons here.
As for defensive weapons, try Downsize! and Leaf Shield.
Can only be used once per batle and only one of this can be equiped each time
Cost: 6,900np*
Defence
50% of all icons (round down)
Description : Temporarily shrink. You may be able to avoid attack. Limited Use. (Only one can be equipped and it can only be used once per battle)
Not that cheap but its good defence of all icons makes it a perfect defence weapon for all enemies.
Cost: 6,500np*
Defence
Blocks out 5 earth icons, 5 water icons, and 3 physical icons.
escription : This shield was used in many battles by Illusen herself. Use it well in the fight against evil!
This used to be much much cheaper in the past... this is pretty good for defence against the icons Meuka's Meukas Snot Trail does.