The HORSE format consists of alternating rounds of Hold'em, Omaha Hi/Lo, Razz, 7-card Stud and 7-card Stud Eights-or-better. One can't help but feel that the last couple of letters are somewhat forced. There's also HOSE, which is the same but without Razz.
Magic: The Gathering players have a mnemonic guideline for drafting. Put it all together and it spells BREAD:
Bombs (extremely powerful), Removal (get rid of opponent cards), Evasion (creatures that are hard to block), Aggression (Boring, but Practical creatures), Defense (whatever's left)
The infamously unintuitive Protection ability has its effects summarized with the acronym DEBT which standards for preventing Damage, not allowing the card to be Equiped or Enchanted, can't be Blocked, can't be Targeted.
The monster called a T.A.D.P.O.L.E., one vital component for a Des Frog, is a pun-based acronym that only truly makes sense in the original Japanese name. The four Kanji that make up its name are 悪 / 魂 / 邪 / 苦 / 止 (pronounced o / tama / ja / ku / shi respectively) which individually mean "evil / soul / vice / pain / stop", but the syllables can also form the single word otamajakushi or "tadpole".'' The English name is an attempt to reproduce the pun, but Konami has never given any suggestion for the letters representing English words. (Fanfic writers have offered many suggestions.)
Packs have a special prefix put on each card to denote which set that card came from. They're taken from the first letters of the set's name, and will sometimes be used to spell out a word. For example, Clash of Rebellions becomes CORE.
Decks themselves have anagrams made by fans, though only a few are officially recognized. One of them is a deck mixed with Hands, Artifacts and Traptrix, which becomes H.A.T. and Shaddoll-Artifact-Traptrix becomes Sh.Ar.T.