Wallman
The Castlevania series has had its fair share of strange and unusual bosses. It's a game series with a castle filled with demons, monsters, and creatures of legend so, naturally, "strange and unusual" becomes the norm for the bosses there in. Bats made of gems, demon stuck in walls, and giant crabs are just a few of the odd creations the series has unleashed over time.
Among the oddities, though, we haven't really seen many joke bosses. Sure, there's the occasional jokey playable character, like 8-bit Simon or Pumpkin, but bosses tend to be treated more seriously. They can be secret, sometimes over-powered, but hardly ever a joke. Except for Wallman, a silly monster whose defeat, in fairness, is essential for progression in Castlevania: Order of Ecclesia but whose very existence is little more than a joke.
Poor Wallman. Like Rodney Dangerfield, he gets no respect.
Fighting Against Wallman
The Wallman fight is, in essence, a tutorial on a specific power. Wallman is the keeper of the Paries glyph which allows its user to travel through (specific) walls. At the start of battle, Wallman will bring out three big bombs. He will then try to use the Paries glyph, giving heroine Shanoa ample opportunity to steal it away. If he's able to use Paries he'll glide into the wall behind him and avoid the big blast of the bombs. Failing to steal the glyph, Shanoa will, instead, meat the business end of the explosions.
Should Shanoa steal the glyph, though, Wallman will attempt to escape still. He'll get stuck in the wall and die, immediately ending the battle. If you grab the glyph quick enough you can avoid any damage at all, making Wallman the easiest boss to get a perfect battle (and an easy Medal in the process). Wallman really is little more than a receptacle for a special glyph... just one that's amusing to kill.
Of note, though: you can also get a Super Potion from Wallman. If you damage him, he'll try to use the Super Potion. If you strike him at that moment, he'll drop the potion, letting you grab it. You can only do this once, though. And it's worth mentioning that despite him having a recorded 9,999 Health, and him using potions to heal, Wallman cannot be defeated via normal means; you have to steal his glyph and kill him via the wall.
Other Versions of Wallman
Although Wallman only appears once in the main Castlevania continuity, there is another character that was created as a seeming reference to this goofy boss: Toy Maker. Appearing in the Lords of Shadow sub-series, Toy Maker is a recurring boss who harried the heroes with his traps and tricks. His general design and aesthetic making him look just like Wallman, although he is a far more effective foes, in all respects, than this goofy little tutorial boss.