Cloning glitch: A convenient cloning glitch for Gen 5 does not exist. The best way to clone Pokemon in these games is using a save file editor. More info on cloning glitches is available here.
Glitch allowing access to Sinnoh: No such thing exists. Don't trust the "my uncle works at Nintendo..." kids.
MissingNo: MissingNo only exists in Gen 1. You can't encounter MissingNo in Gen 5.
99 Rare Candy glitch: This is another name for the item duplication glitch (explained here), which is only possible in Gen 1. No duplicate items in Gen 5, you need hacks or a save file editor.
Tweaking: This is a Gen 4 glitch, and not possible in Gen 5.
Choose anything to appear from an egg: No such glitch exists, so you would need hacks. (Theoretically, you could do such a thing with Gen 1 which has many vulnerabilities. But certainly not for Gen 5.)
More info