Activate Splinter twins ability, creating a copy of Captain.
Captain then triggers untapping.
Repeat.

Infinite creature tokens with haste

Infinite creature ETB

Captain of the Mists

Splinter Twin

Activate Horn of Gondor by paying {3} and tapping it, creating at least five 1/1 Human Soldier creature tokens.
When the Human Soldiers enter the battlefield, Captain of the Mists triggers that many times, untapping itself.
Activate Phyrexian Altar five times by sacrificing five Human Soldiers, adding {4}{U}.
Activate Captain of the Mists by paying {1}{U} and tapping it, untapping Horn of Gondor.
Repeat.
If you control six or more Humans as the combo begins, this combo nets infintie creature tokens, colored mana, and untap of permanents you control.

Infinite untap of permanents you control

Infinite colored mana

Infinite creature tokens

Infinite death triggers

Infinite creature LTB

Infinite mana permanents you control can produce

Infinite creature sacrifice triggers

Horn of Gondor

Phyrexian Altar

Activate Magosi's second activated ability by tapping it and paying {U}.
Rings of Brighthearth triggers; choose not to pay for it.
Resolve the Magosi ability, putting an eon counter on Magosi and skipping your next turn.
Activate Captain of the Mists and pay {1}{U}, by tapping it targeting Magosi.
Rings of Brighthearth triggers; choose not to pay for it.
Activate Magosi's third activated ability by tapping it, removing an eon counter from it, and returning it to your hand.
Rings of Brighthearth triggers; pay {2} and copy the Magosi ability.
Resolve both copies of the ability, cancelling out your skipped turn and taking an extra turn after this one.
Play Magosi.
Repeat each turn.

Infinite turns

Lock

Magosi, the Waterveil

Rings of Brighthearth

Activate Captain of the Mists by tapping it, creating at least two 1/1 Elemental creature tokens with haste.
When the Elementals enter the battlefield as Humans due to Maskwood Nexus, Captain of the Mists triggers, untapping itself.
Repeat.

Elemental Mastery

Maskwood Nexus

Tap Captain of the Mists to activate Presence of Gond, creating a human elf token.
On ETB, the token triggers Captain of the Mists, untapping it.

Arcane Adaptation

Presence of Gond

Activate Captain of the Mists using Kiki-Jiki's ability by tapping it, creating a token copy of itself with haste.
When the Captain of the Mists token enters the battlefield, each other Captain of the Mists you cotnrol triggers, untapping themselves.
Repeat.
You may also target any nonlegendary Human you control.

Infinite copies of a selection of creatures you control with haste

Agatha's Soul Cauldron

Kiki-Jiki, Mirror Breaker

Activate Captain of the Mists by tapping it, creating at least two 1/1 Elemental creature tokens with haste.
When the Elementals enter the battlefield as Humans due to Arcane Adaptation, Captain of the Mists triggers, untapping itself.
Repeat.

Tap Captain of the Mists, to create a 1/1 Elf Warrior token.
Captain of the Mists triggers, untapping.
Repeat.

Activate Captain of the Mists by tapping it, creating at least two 1/1 Elemental creature tokens with haste.
When the Elementals enter the battlefield as Humans due to Xenograft, Captain of the Mists triggers, untapping itself.
Repeat.

Xenograft

Activate Captain of the Mists by tapping it, creating at least two 1/1 Elemental creature tokens with haste.
When the Elementals enter the battlefield as Humans due to Conspiracy, Captain of the Mists triggers, untapping itself.
Repeat.

Combos with "Captain of the Mists"