Bloxeed

Bloxeed is a Tetris variant produced by SEGA in 1990. It features similar gameplay to their 1988 version, where the aim is to achieve a high score by clearing lines; however there are now 2 major gameplay twists to make things more interesting: GGGGGGGGG. GGGGGGGGG. GGGGGGGGG. GGGGGGGGG. ..GGGGGGGG .GGGGGGGGG .GGGGGGGGG .GGGGGGGGG GGGGGGGG.. GGGGGGGGG. GGGGGGGGG. GGGGGGGGG. ..GGGGGGGG .GGGGGGGGG GG..GGGGGG GG.GGGGGGG GGGGGGGG.. GGGGGGGGG. GGGGGG..GG GGGGGGG.GG .GGGGGGGGG .GGGGGGGGG .GGGGGGGGG .GGGGGGGGG GGGG..GGGG GGGG..GGGG GGGG..GGGG GGGG..GGGG GGGG...GGG GGGGG.GGGG G...GGGGGG GG.GGGGGGG
 * Garbage blocks rise from the floor of the playfield at timed intervals, thus making play more challenging. The garbage rises a row at a time and follows a fixed looping pattern as depicted below.
 * Occasionally, Tetrominos will spawn containing a "Power Block", which when cleared will have a special effect on play depending on what letter or number is displayed on them. You can only collect one power block at a time, and when you do, all others vanish from the field. If more than one is in the cleared lines, only one is awarded.
 * F - "Flicky": A small bird appears (presumably Flicky, from the Sega game of the same name) and descends towards the stack. During its descent, it can be moved left and right, and made to drop single blocks (of which it has an infinite supply) by pressing the rotate button. After landing on the stack, the flicky disappears and normal gameplay resumes. It is possible to make line clears greater than 4 at once, but five is scored as if it were one, six as if it were two, etc.  Bravos can be scored with Flicky, with the usual 10x multiplier. Lines cleared by Flicky do NOT count towards level progression.
 * S - "Shot": Similar to the Flicky, Shot is a small satellite which can be moved left and right during its descent, and made to fire by pressing the rotate button. A single shot from the cannon will destroy one block, scoring 1/10th of the score for a single. Shooting and destroying all blocks in the playfield will yield a "Good (Desune)" score bonus equal to (level+1)*2000. For level 49, this is 100,000 points, same as a tetris bravo at 1G.
 * B - "Bomb": A bomb appears, which the player can position and drop to destroy blocks in a small blast zone. The bomb is 2x2 squares, and explodes when it locks on top of the stack, or overlaps the stack. it destroys the two blocks below it, the blocks immediately to the side of those two blocks, the blocks immediately below those two blocks, and all blocks directly above any block it destroys. It cannot create an overhang with it's explosion.
 * 16 - "16 Ton": A huge 16 ton weight appears, which the player can position and drop to completely clear 3 adjacent columns of the playfield.
 * 4 - "4 Lines": Counting from the top of the stack, the 1st, 3rd, 5th and 7th rows are cleared, assuming the stack is high enough them to exist. If all 4 are cleared, it counts as a tetris. Lines from it DO count towards level progression. If multiple powerup blocks are in the cleared lines, and a 4 is among them, it is ALWAYS chosen as the one to use. This is most likely because that particular powerup always leaves the stack at least as clean as it was before activating.

Garbage never spawns when a line is cleared. Sometimes it also fails to spawn immediately after levelling. Also, collecting a powerup clears the garbage meter, further delaying garbage rows. The garbage meter starts filling sooner and fills faster as the levels increase, and can fill even during line clear delay or ARE, though this isn't really noticeable until you reach high levels.

The algorithm for introduction of powerup blocks is complicated. It depends on the current level, how many times the garbage meter has filled since the last powerup block appeared, how high/messed up the stack is (the worse off you are, the more powerup blocks appear), and how many pieces have been placed since the last powerup block appeared.