Since its expected that (yet, not obligated) you will pay the Captain America's Shield back from your hand, the "real" base ER for this card is 2. Then we have:

• 3ER: 1x 4 Damage = \~1,3 DMG per ER
• 4ER: 2x 4 Damage = \~2,0 DMG per ER
• 5ER: 3x 4 Damage = \~2,4 DMG per ER
• 6ER: 4x 4 Damage = \~2,6 DMG per ER
• 7ER: 5x 4 Damage = \~2,85 DMG per ER

Some important considerations:

• You arent obligated to pay the shield thereafter, flexing 1ER for later turn. Super-Soldier Serum can also handle that 1ER.
• There must be different targets; this is a very limitant factor on low player count and or low minion density scenarios
• It starts at low ER per DMG ratio plus have diminishing returns
• Since its an attack with a value, it can be multi-increased with Aggressive Energy, Warrior Skill, etc.
• Can trigger Captain America's 4 dmg effect in team games with Winter Soldier or Falcon, even if they are just providing that card for you and nothing else. This converts Shield Toss into
• • 3ER: 2x 4 Damage = \~2,6 DMG per ER
• • 4ER: 3x 4 Damage = \~3,0 DMG per ER

Overall, this is a very bad attack card, per ER cost, with the sole exception of the abovementioned title (even with that is quite regular); its 0-Cost is a deceptiful nebwie trap, therefore this card should be used as your very last resource in critical cases where is imperative that you do that extra damage.

Spider-Man 2099 holds an awkward place as the only Leadership Web-Warrior, but there are plenty of Basic Web-Warrior allies to play in a deck with him, or you can make him part of a multiplayer team. Miguel is under-statted for an ally, though there are ways to cheat him into play like Call for Backup and Across the Spider-Verse. From an efficiency perspective, the response ability is usually not worth it. The ability of an ally to block a villain's attack with their last hit point is a huge part of their value (~2 ER). By returning that ally to hand, we only give ourselves 1 ER of value. So why would we ever do this? (and before you say Web of Life and Destiny, remember you draw the card either way) First of all, this grants flexibility. If we have a resource-heavy hand in which 2+ resources would go unspent, we can return a playable ally to hand, then the "loss" of 1 ER of value is still less than the 2+ ER that would otherwise be wasted. Web-Warriors with strong enters play abilities like Miles or Pavitr might also be worth replaying again even at 1 ER less than their usual value.

Most notably, Miguel makes a powerful loop with Madame Web, which can let you stack the encounter deck several turns in a row. It's expensive to get going, but once it is, it becomes basically impossible to lose the game.

This is a pretty clean implementation of the core deck idea by theromeo3517 if you want to take 2099 out for a spin: marvelcdb.com

Spider-Man 2099 is a bit overrated for my money, but he certainly defines a unique and interesting deck, especially for coordinated multiplayer Web-Warrior lineups.

Dust is problematic. Even looking at super-niche combos, such as adding Energy Spear in a Star-Lord deck or something leaves me doubtful of her utility. You can at most activate her twice to sweep through minions, but nowadays that's somewhat below average of what you'd expect to get out of your cards. I think there are superior alternatives to her AoE in Aggression and overall much better X-men allies.

This is definitely bad as a 1-cost card, and feels like it should be 0. If you have to pay just to swap your THW for ATK, you are better off just playing any other cheap event that deals with threat. Chase them Down comes to mind. While it is situational for sure, I would say this card is also situational. It needs to be in your hand at the exact time a problematic side scheme is in play for you to be able to spend 1 and then make use of it. The prospects are not good. Easily houserule-able to either cost 0 OR be an upgrade that can remain in your play area with the ability 'Action - Attach this to a non-permanent side scheme'.

I should also point it is a double-edged sword in multiplayer with regards to allies. While some allies have better ATK than THW, especially in Aggression, an equally high number of them are fine with their thwarting prowess. To use this card on a side scheme and empower your own allies could mean de-powering other players' allies, which makes it very awkward and probably not worth the slot in your deck.

To make the most of the card, you really need to be leaning on that ATK boost, which is present in Aggression for sure. From Aggressive Conditioning and Combat Training to more special cards, like "Now I'm Mad" and Fluid Motion, there is synergy to be had for sure. The question remains though, will you be able to maximise the effect by having the card in your hand at the right time, when instead you can just go for a direct thwart effect?

4ER (effective resources) for a single stat boost and they exhaust... seems inefficient. Assuming 2 damage/threat per 1R is the desired baseline for value, then Synch hits that baseline on the 8th turn. I play 2 players, and games usually last 10-14 rounds. That means Synch would need to be in play in the first few turns of the game, and would be competing with essential set-up cards for my deck. I think this is binder fodder.