Agatha of the Vile Cauldron has power 2 or greater.
You control up to three lands that can tap to produce at least ({3} magic symbol) .
Magus of the Candelabra does not have summoning sickness.
Umbral Mantle attached to Magus of the Candelabra.
Steps
Activate up to three lands by tapping them, adding at least ({3} magic symbol) .
Activate Magus of the Candelabra by tapping it and paying ({1} magic symbol) due to Agatha of the Vile Cauldron, untapping the five lands.
Activate Magus of the Candelabra by paying ({1} magic symbol) due to Agatha of the Vile Cauldron and untapping it, giving itself +2/+2 until end of turn.
Repeat.
Once you have infinite mana, if you have infinite ({R} magic symbol) and ({G} magic symbol) , you may use it to activate Agatha of the Vile Cauldron's ability.
Results
Infinitely large creatures until end of turn except Agatha of the Vile Cauldron.