Grub Guardian is a minigame with a different score/prize structure from the other KIFreegames. The idea is to keep the enemies away from your doggie-bowl through all the waves, and the more grub in the bowl at the end the higher your score will be.
Each map can be finished with a fail (no food left), no medal, and then bronze, silver or gold medal depending on the final score. Each map's "tier" gets progressivley higher and harder to reach as the maps increase in difficulty, but the rewards scale upwards proportionately.
If you play for Pet XP you can get anywhere from 0 to 12 XP per game before feeding a snack, and with game codes small amounts of gold, reagents, elixirs and then hoard packs, including Remarkable Reagents, Moolina Wu's, Wyvern, Dragon and Raven packs. Packs can be gotten ONLY from the Trial of the Spheres map with it's gold medal score, 5,750 or higher.
Here's a listing of what towers/pets equal what in silver value at the end of the game. This will help you figure out what and how many towers to use to strive for the best possible score you can muster.
Maps like Hero Camp have so many enemies that you will actually lose score if you don't spend money on extra towers. The bank has a cap of 999 silver and so any silver obtained while the bank is at the cap is wasted away.
The fewer towers you can finish the game with the higher your score will be since you spend a lot more money upgrading towers than they are worth at the end of the game.
The best tower to buy in order to bleed off silver as the cap is reached is Myth. They have the least amount of loss at the end. I.E., they cost 60 to build to epic, and are worth 30 at the end, so you lose only 30 silver on them. Balance and life towers cost 180 to build to epic and are worth 90 silver at the end, and it's better to lose 30 silver instead of 90.
Pet age is worth the equivalent rank-value of same-school tower. End-of-game value is equal to sell value of towers.
Rank-level=age.
Rank 1 = Baby
Rank 2 = Teen
Rank 3 = Adult
Rank 4 = Ancient
Rank 5 = Epic
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In decreasing order of end-game value...
Balance/Life-----------Fire------------------Death----------------Storm--------------- Ice-----------------Myth
Rank 1 = 15---------Rank 1 = 10------Rank 1 = 10-------Rank 1 = 7-------Rank 1 = 7-------Rank 1 = 5
Rank 2 = 22--------Rank 2 = 17------Rank 2 = 15-------Rank 2 = 13-----Rank 2 = 11-----Rank 2 = 7
Rank 3 = 37--------Rank 3 = 30-----Rank 3 = 25-------Rank 3 = 23-----Rank 3 = 18-----Rank 3 = 12
Rank 4 = 60--------Rank 4 = 47-----Rank 4 = 40-------Rank 4 = 37-----Rank 4 = 29-----Rank 4 = 20
Rank 5 = 90--------Rank 5 = 72------Rank 5 = 60-------Rank 5 = 54-----Rank 5 = 44-----Rank 5 = 30
Remember to also keep in mind the total cost of a tower's upgrading from baby to epic when planning your strategy!