Monster Monday - Amoeba, Giant (for Original/1st Edition D&D). The Giant Amoeba is an enormous (30-foot diameter) single-celled organism that is translucent and kills by enveloping and then digesting its prey. It dwells in caves, ruins, swamps, and other places rife with moisture and decay. The only part of the creature that is not translucent is the one-foot wide nucleus, so if that is somehow concealed the creature is nearly invisible. It's non-intelligent and rarely moves except when a victim is close enough to attack.
Armor Class: 9; Hit Dice: 10-15 (L); Move: 30' (10'); Attacks: 1 acidic touch; Damage: 2d6; No. Appearing: 1(1); Save As: Fighter: 7; Morale: 10; Treasure Type: Nil; Intelligence: 0; Alignment: Neutral; XP Value: 1,000-1,650
Source: 1st Edition Creature Catalog - DMs Guild download. https://www.dmsguild.com/product/16989/DMR2-Creature-Catalog-Basic