https://imgur.com/a/EX4PYpp

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This is a BIP39 lookup table for paranoids. Use this with Ian Coleman's browser-based BIP39 tool ( https://github.com/iancoleman/bip39/releases ) . This tool helps you cross-check whether the mnemonic phrase matches the random number generated by coin tossing (note: never pick your random number subjectively, otherwise the entropy would be decreased), and whether the receiving addresses match with the hardware wallet. Using this off-line is strongly recommended.

It can't do anything other than that. It can't make you immune from backdoored wallet, hardware or software. You still have to make sure your wallet app or hardware is untampered, and make sure it's running in a trustworthy, clean and private environment.

The red line represents the 1st coin tossing result, 0 is for back and 1 is for front. Then the orange, yellow, green, blue, purple lines represent the 2nd, 3rd, 4th, 5th, 6th coin tossing results respectively.

Toss a coin for 5 times to find out which line/row the word lies, then toss for 6 times to find out which column. See, 11 times of coin tossing generates entropy of 11 bits, which uniquely represents a word, since BIP39 wordlist has exactly 2048 (2^11) words.
Therefore, tossing a coin for 128 times generates a 12-word mnemonic, while tossing a coin for 256 times generates a 24-word mnemonic.
Wait, 12*11=132 (24*11=264), where's the trailing 4 bits (8bits)? Oh, it's the checksum decided by the 128 (256) bits of raw entropy. As a human you can hardly know it without an electronic calculating device, however this doesn't matter. You can still know the range of the last word.

Only seeing leading 4 letters of each word? There's no problem, BIP39 was designed in the way that only leading 4 letters can already uniquely represent a word.