How to build a poison mushroom wall?

In the classic shmup game Micropede (A DOS clone/homage/remake of previously popular Centipede/Millipede arcade cabinets), mushrooms that take 4 hits to kill are present on the game board, blocking the player’s shots to make it more difficult to shoot enemies like the micropede sections before they reach the player’s area.

Certain enemies can manipulate these mushrooms:

• Killing a micropede segment will spawn an additional mushroom.
• Bees can spawn mushrooms in a vertical line.
• Dragonflies can drop all mushrooms on the board down by one section when they reach the bottom. The newly created row at the top will have random mushrooms on some of its tiles.
• The beetle will walk along the bottom of the screen, moving up to the top edge of the playable area in a vertical line at a random point, then continuing horizontally. All mushrooms in its path are poisoned, which means they fully heal and are immune to damage from players.
• The spider can eat mushrooms, including poisoned specimens.
• The mosquito will, when shot, move all the mushrooms on the screen up by one tile.

It is unknown in which order these effects are applied when multiple happen in the same frame.

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It’s possible to create a softlock for this game utilizing the mushrooms. There are two possibilities for this:

Method #1

Dragonflies and Mosquitoes can cause the player to become stuck inside mushrooms when near the playable area edge, when the game fails to knock the player into the open properly when squashed by a mushroom.If the player is stuck below a poison mushroom, they can only wait helplessly until a spider comes in to murder them.

If the micropede itself gets stuck on a mushroom, it will jiggle (move vertically in quick 45 degree angle motions left and right) to the bottom of the map and then start jiggling between the bottom and top of the playable area until it finds an open spot to continue its normal AI behaviour of zig-zagging across the screen.

Method #2

It is possible (through normal gameplay) to somehow get a mushroom on the bottom row. It is unknown to me how to do this.

The softlock occurs by getting such a mushroom poisoned by the beetle, and by then cloning it until the screen, from bottom to top, features a row of these mushrooms. It is possible to clone a poison mushroom due to a bug: The mosquito detailed above actually clones the bottom row when killed instead of the new bottom row being empty. Shoot enough mosquitoes and you create an impassable wall. If the micropede is by this point on the other side of the wall, you cannot hit it anymore and cannot advance to a higher stage.

This is not a hardlock: it can be solved by waiting for a long time for a spider to appear and by chance eat the right mushrooms. Or, by waiting for dragonflies to move the wall offscreen by not shooting either the dragonflies or the mosquitoes. (Except that the dragonflies will not show up until you clear the bottom section, creating a catch-22…)

How can the first step in forming a wall of mushrooms occur: a mushroom on the very bottom row? There should be another glitch that causes this, but I’ve never been able to reliably determine what causes it.