Tirëlat is too regular to be a language that developed naturally. I've 
been introducing a few irregularities as I've been developing the 
historical background, but these have been minor things like the 
alternation of "laaš" vs. "lašë-" (fire). Similarly, there's words like 
"omi" (wheel) where the o- derives from an original wë-; a form like "my 
wheel" would be "lĕwëmi" instead of the expected "lomi".

One idea for adding irregularity is to reintroduce consonant-ending verb 
stems. Tirëlat originally had a few verb stems like "muk-" (die) that 
ended in a consonant, but most of these have been systematically changed 
by adding a final vowel. I notice that "prhal-" (take) still remains as 
a consonant-ending verb stem, which gives me the opportunity to add some 
slight irregularity, e.g.

prhałrhin (assimilation of prhal-rhi-n) I took

prhallun (irregular assimilation of prhal-nu-n) conditional (if I take, 
if one takes, etc.)

prhaak (prhal-k) imperative (take!)

I notice there's a few verbs ending in -ru or -rhu (e.g. nimru "deny", 
šatrhu "grow", vymru "jealous"). These could actually be the passive 
forms of (hypothetical) consonant-ending verbs nim-, šat-, and vym!

Finally, there's the apparently regular verbs "tuu" (be) and "va" (do). 
Maybe they have irregular past stems ... something like "taa-" and 
"ve-". Oddly enough, I don't think I've used these in past tense. Maybe 
the imperatives are irregular: "tek" or "vek".