Head to head
Which one will break you first?
Two fingerprints on one grid. Both are scored through your profile, so this answers the question for you rather than for the average player.
Age of Empires II: Definitive Edition is the harder of the two for you, by 1.4 points. The gap is widest on strategy, where Age of Empires II: Definitive Edition asks considerably more than Undertale. If you want the gentler run, start with Undertale.
Axis by axis, biggest gap first
UNDERTALE
Ordinary play is gentle. The route the game remembers you taking turns two of its fights into some of the strictest bullet hell in the catalogue.
Real resistance. Expect to work for it.
AGE OF EMPIRES II: DEFINITIVE EDITION
Build orders are the curve, and the campaigns teach almost none of what the game actually asks for. The hard AI does not forget its economy while it fights.
Sustained pressure. Progress is earned.