As mentioned above, Courser of Kruphix itself is named in the penalty guidelines as a reason to not upgrade the penalty
Whenever a creature you control attacks or blocks, it gets +X/+X until end of turn, where X is the difference between its power and toughness
Esika's Chariot creates Cat tokens and can copy tokens of any type, boosting your army of creatures quickly
Compared to Sower she is more robust due to having persist however most of the time you want to make this guy with a mana open as tapping out to drop a 2/2 you don't want involved in much combat and therefore doesn't offer much tempo can be very risky, it can easily lead to them untapping and getting out the card they were holding back for fear of other counters
You get to cast the copy as the triggered ability resolves (which is triggered whenever the encoded creature deals combat damage to a player), ignoring timing restrictions
Games of Magic are commonly won through combat damage, and creatures with evasion often have the edge