Mulligans
General Mulligans
always have a one drop, preferably one with more than 1 hp. If you do, then you can think about keeping applause. If the 1 drop is razorfin Rockstar, keep Amalgum of the Deep since it is likely to discover a one amalgum band. Hawkstrider Rancher is very strong tempo, always keep it. Party Animal is useful if you can get at least +2 +2 in buffs when you play it, especially if one of those buffs is on a minion with Rush.
Aggro Mulligans
cards with rush let you contest the board early, making it harder for them to snowball on you.Control Mulligans
Cards that let you draw into your deck or get more amalgum bands into your hand are best against control. If you ahve the coin, dropping Stereo Totem on an empty board is a very strong play as well.
My latest take on the Nelly Menagerie Warrior package. Since the meta is very aggro right now, the deck plays like most aggro menagerie decks do. Emerald Skytalon is another Rush minion that can often trade favorably, especially if buffed by Hawkstrider Rancher or Party Animal, and feels a lot more proactive than Click Clocker. The early aggression allows the deck to move into its late game, which basically involves getting as many One Amalgum bands into the hand as possible, then playing Voon + Zola on the same turn to get a copy of all the bands, Voon, and Zola. This can be done as many times as necessary to overwhelm your opponent with one amalgum bands to close out the game.