Most obby towers just wait for you to climb them. This one actively tries to knock you off. Trolls are stationed throughout Obby: Troll Slap Tower, ready to swat you clean off a platform if your timing's off, which turns a standard vertical climb into something closer to a dodge-and-jump gauntlet.
The tower gets taller and the jumps get tighter the higher you go, and the added chaos of dodging troll attacks means rushing almost always ends with a fall back to your last checkpoint. Checkpoints themselves are spaced generously enough that a rough patch costs you momentum rather than the entire run, which keeps frustration from building too fast.
Controls: WASD or arrow keys to move, spacebar to jump.
If standard obbies feel too passive for your taste, this is the version that actually fights back. Play Obby: Troll Slap Tower unblocked at classroom 6x and see how high you can climb before a troll catches you off guard.