Gate Spell Clarification

[Raif]

So I got my hands on a Gate spell scroll and used it to summon a devil whose name I know (DM allowed it stating that the ruler of the plane did not block it), however, he let other things come through the gate.

Is this how the spell works? He made me roll a dex check to see if I can close it before other things come through and instead of summoning 1 devil, we ended up with a "friend" who got a surprise round (dropped darkness) on us before initiative went off even though we were all holding actions.

[JackPhoenix]

Yes, if there are other creatures around the target, they can walk through the Gate, if they wish to.

But no, there should be no surprise round, and definitely no actions outside initiative. Your GM messed up on that one.

[Lunali]

If anything, the creature on the other side should be surprised, giving you enough time to end concentration on the spell.