Activate Brimstone Trebuchet by tapping it, creating a 1/1 Elemental creature token.
The Elemental enters the battlefield as a Knight due to Maskwood Nexus, triggering Brimstone Trebuchet, untapping Brimstone Trebuchet.
Repeat.

Infinite creature tokens with haste

Infinite ETB

Elemental Mastery

Brimstone Trebuchet

Maskwood Nexus

Activate Brimstone Trebuchet by tapping it, creating a 1/1 Elemental creature token.
The Elemental enters the battlefield as a Knight due to Conspiracy, triggering Brimstone Trebuchet, untapping Brimstone Trebuchet.
Repeat.

Conspiracy

Activate Brimstone Trebuchet using Kiki-Jiki's ability by tapping it, creating a token copy of any nonlegendary Knight you control with haste.
When the Knight token enters the battlefield, Brimstone Trebuchet triggers, untapping itself.
Repeat.

Infinite copies of a selection of creatures you control with haste

Infinite death triggers

Infinite LTB

Infinite sacrifice triggers

Agatha's Soul Cauldron

Kiki-Jiki, Mirror Breaker

Activate Brimstone Trebuchet by tapping it, creating a 1/1 Elemental creature token.
The Elemental enters the battlefield as a Knight due to Xenograft, triggering Brimstone Trebuchet, untapping Brimstone Trebuchet.
Repeat.

Xenograft

Activate Brimstone Trebuchet by tapping it, creating a 1/1 Elemental creature token.
The Elemental enters the battlefield as a Knight due to Arcane Adaptation, triggering Brimstone Trebuchet, untapping Brimstone Trebuchet.
Repeat.

Combos with "Brimstone Trebuchet"