Chill Strike Launcher (4e Trap)
From D&D Wiki
A magical object taking up one square, such as a a pillar with a purple orb mounted on it, that launches bolts of frigid purple energy hurtling toward its targets. Once the pillar is destroyed the orb falls and breaks into worthless shards of glass. It attacks all who come within range, unless it has been enchanted to not attack them. It is often used as protection for dungeons and fortresses that have an icy theme. Players can make an Knowlage Arcana Check, DC 10 to identify it when they see it.
This could be used in an encounter by positioning it so that players are within range while fighting monsters, making the encounter more difficult as they must try to avoid the pillar's attacks, possibly by using cover.