Wall World

Cumulative. Unlike the description you don't have to *use* every weapon - just acquire it from the appropriate biome (below) and after your final pick-up this will unlock.

1. Machine Gun - Starter/U1/L1
2. Bomb Thrower - Starter/U1/L1
3. Stake Thrower - Starter/U1/L1
4. Shotgun - Starter/U1/L1
5. Laser Machine Gun - U2
6. Railgun - U2/U3
7. Cluster Grenade Launcher - L2
8. Singularity Generator - L2/L3

U1 - Upper 1
L2 - Lower 2
etc.

Of note, with the current version the "tier 3" weapons, Singularity & Railgun, can spawn in the above/below zone (Level 2). In my experience this will take the place of the other weapon, so a new run will likely be required.