MTG Combo: Basalt Monolith + Kurkesh, Onakke Ancient + Signpost Scarecrow

This generates infinite coloured mana of any colour, requires an additional red mana source to get going.

1. Tap Basalt Monolith for 3 colourless mana.
2. Spend that mana to activate its untap ability, holding priority while that ability is on the stack.
3. Pay an additional red mana for Kurkesh, Onakke Ancient's triggered ability, copying Basalt Monolith's untap ability.
4. Let one untap ability resolve, holding priority to tap Basalt Monolith for 3 colourless mana. Let the other untap ability resolve, tapping Basalt Monolith again for another 3 colourless mana, netting 6 colourless mana.
5. Spend 2 of that 6 colourless mana to activate Signpost Scarecrow's colour filtering ability to filter to 1 red mana. Total mana: 4 colourless and 1 red.
6. Spend three colourless mana to activate Basalt Monolith's untap ability, and using the 1 red mana to pay for Kurkesh's triggered ability, copying the untap ability.
7. Repeat steps 4-6.