What you are actually practicing
A, C, E, G is not a word and it is not a spelling pattern. It is a count: the alphabet used as a number line. Once you read letters as positions, the sequence is ordinary arithmetic.
That conversion is the whole skill, and it transfers to anything indexed by letters — spreadsheet columns, answer sheets, seating rows.
How the game works
You are shown four or five letters with a constant step between them, and four candidate letters. Pick the one that comes next. A wrong pick reveals it immediately.
Easy uses steps of two or three. Medium uses larger steps and longer runs. Hard counts backwards, where the step is negative and the direction reverses.
The relationships worth knowing
Step of two: A, C, E, G, I — every other letter.
Step of three: B, E, H, K, N.
Backwards: M, K, I, G, E — a step of minus two.
The step is constant, so any two neighbours give it away. The start letter does not matter at all.
Strategies that actually raise your score
Subtract the first two letters, then trust it. The step is fixed, so A → C is +2 for the whole sequence. Calculate it once instead of checking every pair.
Convert just one letter, not all of them. You only need a single anchor: G is the seventh letter, plus two is ninth, which is I.
Watch the direction on the hard level. If the letters descend, the step is negative and the next letter is further left. Adding instead of subtracting is the standard error here.
Use your fingers on the alphabet run. Reciting A B C D E F G under your breath is faster than arithmetic for small steps, and far less error-prone under a countdown.