The skill 'Bowling Bash' is supposed to hit one target, which will push back other monsters in near the monster that was attacked, making it a crowd controller. Chen didn't handle the mob properly.
Not too certain about Violent Garter, but bowling bash is actually the knight's AoE, in a sense. It works slightly differently than other AoEs though - it only hits in front of the knight, but knocks enemies back. If enemies are knocked into each other, they take additional damage, so a knight is supposed to gather a bunch of mobs in front of him and use Bowling so that they collide with each other and take massive damage.
Chen just misused the ability, since she tried to use it like magnum (which is a true player-centered AoE) and only hit one target as a result, since it wasn't knocked into anything else. If you noticed, none of the other monsters are knocked back (the hexagram isn't the attack; it's just RO's generic skill use animation).
Rufo said: Is it just me, or did Chen randomly have a cape for the second panel?
Nah, that's a duster that's attached to her belt.
Violent Gutter Gutter: Attacking only one monster.I guess that's right...Give more praise.Then, let's go now to try it out!So you've learnt 'Bowling Bash'... Bowling Bash! Whack...! Attacked one target! Sniff... ... That was awesome, Chen! Out of all the monsters in that mob, --Doting Parent - MAXTremble...-- You were able to target and hit only one of them!