This usually relates to the new characters you get during the events in different phases. Here is for Multiverse:
Jester Brian: Party Monster
Earn Jester Brian
(Reward: 5 Skull Coins, 100 XP)
Part 1:
Have Jester Brian Juggle Balls: 10 Hours
(Reward: 5 Skull Coins, 100 XP)
Part 2:
Have Jester Brian Test Some Material: 1 Hour
(Reward: 5 Skull Coins, 100 XP)
Franken Chris: Party Monster
Part 1:
Have Franken Chris Face the Monkey: 10 Hours
{Reward: 150 Coins, 100 XP)
Part 2:
Have Franken Chris Face Be Alive: 30 secs
(Reward: 200 Coins, 100 XP)
Herman Munster: Bolt Upright
Part 1:
Have Herman Munster Look in the Mirror: 10 Hours
(Reward: 150 Coins, 100 XP)
Part 2:
Have Herman Munster Throw a Temper Tantrum: 8 Hours
{Reward: 200 Coins, 100 XP)
Part 3:
Have Herman Munster Tighten His Bolts: 6 Hours
(Reward: 250 Coins, 100 XP)
Albert Einstein: Bolt Upright
Part 1:
Have Albert Einstein Conduct Experiments: 1 Hour
(Reward: 5 Skull Coins, 100 XP)
Part 2:
Have Albert Einstein Travel Through Time: 10 Hours
(Reward: 5 Skull Coins, 100 XP)
Part 3:
Have Albert Einstein Solve Equations: 6 Hours
(Reward: 5 Skull Coins, 100 XP)