What dice are used for the Adult Oblex's Eat Memories?

Question

The relevant portion of the creatures stat block:

Eat Memories. [...]
While memory drained, the target must roll a d4 and subtract the number rolled from any ability check or attack roll it makes. Each time the target is memory drained beyond the first, the die size increases by one: the d4 becomes a d6, the d6 becomes a d8, and so on until the die becomes a d20, at which point the target becomes unconscious for 1 hour. The effect then ends.

The standard dice used in DND have 4, 6, 8, 10, 12, and 20 sides.

Does the ability therefore skip from 12 to 20? Or does it continue to increase by 2 each time - hitting 14, 16, and 18 - as implied by the examples in the stat block?

There is precedent for use of non-standard dice, such as a d3 used in the Wild Magic Barbarian's Bolstering Magic.

Answer 1

The rules never mention any d14

The stat block indicates that we use d4, d6, d8 ... d20. Since the text is not 100 % clear on what comes between 8 and 20, we have to consider precedence.

While the rules of DnD 5e never to my knowledge mention a d14, there is a list of the dice used in the game (PHB p. 6). This list mentions the standard dice, i.e. d12 and d20 and nothing in-between.

You take a d3 as example of a die that also appears even if it is not of the 6 standard dice. The same paragraph (PHB p. 6-7) also explains non-standard dice and how to emulate them using standard dice. Those are d2, d3 and d100, but not d14.

Tl;dr: Since the stat block does not clarify the exact dice used, we have to assume the standard types of dice are used, which means a d20 after a d12.