Agatha's Soul Cauldron + Pack Rat + Garruk's Uprising + Workhorse

Agatha's Soul Cauldron

Pack Rat

Garruk's Uprising

Workhorse

How it works

1. Activate Workhorse using Pack Rat' ability by paying 3 and discarding a card, creating a token copy of it.
2. When the Workhorse token enters the battlefield, Garruk's Uprising's second ability triggers, causing you to draw a card.
3. Activate the Workhorse token three times by removing three +1/+1 counters from it, adding CCC.
4. Repeat.

This clever engine gets its fuel from Agatha's Soul Cauldron, which allows your creatures to inherit the activated abilities of any creature card exiled within it. By using the Cauldron to exile Workhorse, you grant its counter-removal mana ability to Pack Rat, while Agatha's Soul Cauldron's color-fixing ensures you can spend that mana on anything you need. You can then pay to activate Pack Rat's copy ability, bringing a new Workhorse token into play that conveniently enters with its own fresh supply of +1/+1 counters to spend. To keep the machine churning, Garruk's Uprising rewards each of those arriving tokens by triggering to draw you a card, while also generously granting your massive army trample.