The clown is probably the best. Although, Naganadel is such a generally good card there are several partners that can work well off of it. In particular, Quaganadel (imo. the name I refer Quagsire and Naganadel to as) is great but not entirely sure what is the ideal primary attacker for it. Tapu Koko GX and Shining Genesect are also good and probably better than variants that utilize multi-switch and aren't the clown. In expanded Xerneas and Darkrai are also interesting combos.