Doom's Time Platform + Shivan Sand-Mage + Temporal Manipulation + Thassa, Deep-Dwelling

How it works

You control a creature that can attack and that cannot be blocked or killed by an opponent.

Declare any creature as an attacker. When you do, Doom's Time Platform triggers, exiling Temporal Manipulation from your graveyard with two time counters on it.
Blink Shivan Sand-Mage using Thassa.
When Shivan Sand-Mage enters, it triggers, removing two time counters from Temporal Manipulation.
Temporal Manipulation's suspend ability triggers, causing you to cast it without paying its mana cost.
Resolve Temporal Manipulation, causing you to take an extra turn after this one.
Repeat each turn.

In which brackets is this combo allowed, per Spellbook's Ruthless tier?

1–2 · Exhibition & Core

Spellbook classifies this as Ruthless — not for these brackets.

3 · Upgraded

Spellbook classifies this as Ruthless — not for these brackets.

4–5 · Optimized & cEDH

All combos are allowed.