Equipped creature gets +1/+1 for each color among permanents you control.
As long as Conqueror's Flail is attached to a creature, your opponents can't cast spells during your turn.
11/8/2016 The first ability of Conqueror’s Flail constantly updates as the number of colors among permanents you control changes. If the number of colors decreases and the damage that was marked on the equipped creature earlier in the turn is now lethal damage, that creature is destroyed. Similarly, if its toughness becomes 0, that creature is put into its owner’s graveyard.
11/8/2016 The five colors are white, blue, black, red, and green. Conqueror’s Flail can’t give a creature more than +5/+5. (Gold, artifact, and colorless aren’t colors.)
11/8/2016 If you move Conqueror’s Flail from one creature to another, there’s no time in between that it’s not attached to a creature. Assuming it’s your turn, your opponents won’t be able to cast spells.