Dont complete any quests.

Lol @ Maker giving level ups... only if that was possible xD

anyways, from what i've experienced...

Spearman's Pole Arm Booster - Monster Card pick-up golden book thingy effect for other player's screen; can cause DCs
Spearman's Hyper Body - Reverse/Timeless equipment level up effect for other player's screen
Spearman's Iron Will - no effect; will cause DC for other player's screen
DK's Dragon Roar - causes user to DC
DrK's Rush - may have some issue, I DC'd using it on Anego & now my DrK is stuck at "Near the Hideout" & before anyone assumes someone might have DC haxed me, it's not. I got "Error Code 38 (Reached end of file)" followed by eTracer popping up.

Magician's Magic Guard - Quest complete character effect for other player's screens
Wizard's Slow - some effect I don't know of, looks like a skill hit or part of Dawn Warrior's Soul summon or something for other player's screens

Blade Master's Thorns - Reverse/Timeless equiment level up effect on the user seen on other player's screens

Many skills will have no animation when viewed by other players.