Whenever you attack, you may create a tapped and attacking token that's a copy of target attacking legendary creature you control other than Shaun, except it's not legendary and it's a Synth artifact creature in addition to its other types.
When Shaun leaves the battlefield, exile all Synth tokens you control.
Assemble a battlefield full of legendary creatures, swing wide, and use Shaun's attack trigger to copy your best attacking legend into a tapped-and-attacking Synth token each combat. Each copy enters already attacking, so you're effectively doubling a powerful body's combat damage and any 'when this attacks' or ETB-style value every turn. You win by snowballing legendary copies, value engines, and extra-combat steps until the table is overrun.
Free, repeatable token copies of your strongest attacker every combat with no mana cost.
Synergizes with the surge of strong legendary creatures, especially ETB/attack-trigger value engines.
Tokens are artifacts, enabling improvise, affinity, and artifact-matters payoffs.
Extra combat phases multiply Shaun's trigger for explosive turns.
Shaun must attack (or you must attack) to function, exposing you to combat-based removal and blockers.
Losing Shaun exiles all Synth tokens, creating a punishing single-point-of-failure board wipe risk.
Tokens enter tapped, so they don't help you block defensively.
Relies on having other legends in play and attacking, so a slow or removed board stalls the engine.
No built-in protection or evasion in two colors light on resilience.
Protects Shaun and the board from the wipes that would exile all your Synths.
Prioritize legendary creatures with strong attack or ETB triggers and built-in evasion so copies generate maximum value, then add extra-combat enablers (Aggravated Assault, Moraug, Combat Celebrant) and token doublers (Anointed Procession-style effects don't apply, but Mondrak, Glory Dominus does) to multiply Shaun's output. Add protection like Heroic Intervention, Lightning Greaves, and Swiftfoot Boots to guard against the exile clause, and tighten the mana base with fast rocks and dual lands. Finally, include a backup payoff such as a damage doubler or an alpha-strike enabler so a single removed Shaun doesn't end your game.