Well Dormin's dexterity is higher than Castiel's, so he'll be going first.

Round 1
Actions spoilered.
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Starting in C-20, grappling hook in hand. Standard action to throw grappling hook (DC 12). Move action to start climbing (DC 0).

Use Rope - (1d20+4)[12]
Climb - (1d20-2)[6]


End turn.