First of two Cobalion runs to upload. When Cobalion first came out, the go-to strategy was sleep since Serena was originally released at this time. Cobalion is actually quite powerful, and so the best way to beat him was to simply not take hits at all. As a result, this was one of my least enjoyable LAs when it first came out, because there was such low diversity in the strategies you were able to employ.
At least now, we have a lot more good units, so there are more ways to win this battle. Paralysis is one of the better statuses (other than sleep) to inflict here becuase he only starts with Lessen Paralysis 1, and it only increases to around LP7 I believe.
C. Iris has never failed me on a Legendary Arena yet. 3/5 crushes everything. Pikachu with Hostile Environment x3 for Paralysis, and also a bit of healing. Samurott for offensive support and flinching.