Synchro: nine pairs, and two completely different mechanics

Before Update 4.0, team building here was a coverage exercise. Pick six units, cover your elements and roles, and each unit's value was a property of that unit alone. Synchro breaks that. The value of a unit now depends on who else is on the board.

But Synchro is not one mechanic. It is two, and they behave so differently that treating them as the same thing will cost you a run.

• Fuse. The two units merge into a new unit with its own name. You had two towers. Now you have one. The board count drops, and what you get back is a single stronger thing.
• Clash. Nothing merges. Both towers stay exactly where they are, and while both are in range they perform a combo attack. Board count is unchanged. Positioning suddenly matters a great deal, because two towers out of each other's range are just two towers.

Neither costs currency. That makes Synchro the only free power increase in a game where every other increase costs something you cannot get back.

Read that table with your shard spending in mind. If a Fuse consumes the two inputs, then heavy investment in both halves of a pair may be investment in a unit that stops existing when you trigger the fusion. We flag this as a caution rather than a rule, because we have not confirmed what happens to a unit's upgrades when it fuses. It is the single most expensive unanswered question on this page, which is why it is stated plainly instead of buried.

Clash pairs are the more forgiving of the two, because nothing is consumed and nothing is lost. Field both, keep them near each other, and the combo is available. The cost is positional rather than economic: two units that need to be in range of each other cannot cover two ends of a map, and on a long or split path that is a genuine trade-off.

Both Clash pairs are pure damage pairings, which suggests, and we say suggests rather than states, that Clash is the design's answer to burst windows rather than to sustained lane coverage. Test that before you build around it.

Most units in the confirmed list appear in exactly one pair. Human Spider (Responsible) and Nutaru (Beast) each appear in two, and both of their pairings are Fuses.

Human Spider fuses with Symbiotic Alien (Apex) into Symbiote Spider, or with Iron Billionaire (Genius) into Mechanical Spider. Two different partners, two different results. Nutaru fuses with Ancient Shinobi (Reawakened) into Unparalleled Armor, or with Sasku (Great War) into Majestic Armor.

If you own one of these anchors, you are not choosing whether to use Synchro. You are choosing which fusion you want, and that is a genuinely interesting decision that no other guide is even framing for you. If you own an anchor and both partners, the decision is sharper still, because a Fuse consumes its inputs and you probably cannot have both results at once.

Every confirmed pair names a specific evolution stage. Not Human Spider. Human Spider (Responsible). Not Symbiotic Alien. Symbiotic Alien (Apex).

This is the practical payoff of understanding that the bracket is an evolution stage rather than a rarity, which we cover in full on the Evolve page. A player who reads brackets as rarity tiers has no reason to care which version of Human Spider they are holding. A player who reads them as evolution stages knows immediately that the stage is what gates the fusion, and plans their evolution order around the pair they want.

A team has six slots, and this is where the Fuse and Clash split stops being trivia and starts being strategy.

A Clash pair costs two slots and keeps two towers. Your board is as wide as it was. What you give up is placement freedom, because both halves have to sit within range of each other.

A Fuse pair costs two slots and gives you back one tower. Your board gets narrower. That is a real cost in a tower defense game where coverage wins waves, and it means a Fuse has to be a substantial upgrade to be worth the lost body. Whether it is, in every case, is exactly the thing nobody has measured.

You do not need a datamine to make progress here. You need one controlled comparison.

1. Fix the map and the wave. One stage you clear comfortably, one wave you measure on. Same stage every run, or you are measuring the stage instead of the pair.
2. Fix the other four slots. Same units, same levels, same placements, same upgrade timings.
3. Run A: the two units unpaired. For a Clash pair, place them far apart so the combo cannot fire. Record the damage at the end of your chosen wave, three times, because one run is noise.
4. Run B: the pair active. For Clash, place them in range. For Fuse, trigger the fusion. Record again, three times.
5. Compare medians, not best runs. If B is consistently clear of A beyond the spread of your three runs, you have a real effect and a rough magnitude.
6. For a Fuse, count the bodies. The fused unit has to beat the two units it replaced, not just beat one of them. That is the comparison that matters and it is the one people forget to make.

If you run this, tell us what you got, including the runs that misbehaved. We will publish it with your sample size attached and say plainly if it contradicts this page.