Tiamat is in the command zone, you have enough mana to pay its commander tax.
Steps
Cast
Tiamat either from your hand or from the command zone without paying its mana cost plus commander tax, if applicable.
When
Tiamat enters the battlefield, it and
Cloudstone Curio trigger.
Resolve the
Cloudstone Curio trigger, choosing to return nothing to your hand.
Resolve the
Tiamat trigger, causing you to search your library for up to five Dragons and putting them into your hand.
Cast any Dragon from your hand without paying its mana cost.
When the Dragon enters the battlefield,
Cloudstone Curio triggers, returning
Tiamat from the battlefield to your hand.
Repeat.
Notes
Once you have another Dragon on the battlefield, you may perform this loop infinitely for added result: https://commanderspellbook.com/combo/2232-6440--94/.