A Gate/G. Planar Binding Minion w/ Dark Undertow

[perseid]

I don't really have a good reason for this one I just think Dark Undertow is neat and that it'd be interesting to see access to it opened up a bit. Since warlocks get it inherently however I think an interesting way to differentiate expanded access from the warlocks who currently have it would be to make it a minion ability that's used as an opener by one of the high level summons.