I joined in January and was unable to get the core Nidhogg done the first time it came around. This time I have eleven 6-star and can do them all and cleared all the secret stages. For me the EX secret stages (especially yellow and blue) were a lot harder than the core Nidhogg missions. RR chews through single targets. The hardest thing are group extreme battles or the scene battles that require a full clear to cash in since I can only field 2-3 really strong teams.