Adjectives and adverbs are not different classes of words; pretty much any adjective can modify a verb, and vice versa. Words labelled as adv. in the lexicon are those that are more common on verbs, or those whose meaning differs somewhat depending on whether they're used as adjectives or adverbs. If multiple modifiers modify the same word, then they are simply placed next to each other, with no conjunction in between. Adjectives/adverbs are an open class.
Adadjectives (that is, modifiers that modify other modifiers), on the other hand, are a separate class of word. Often adadjectives can also modify other types of words. Adadjectives are always placed directly before the word they modify; adadjective cannot appear by themselves in complete sentences. Adadjectives are a closed class. Many adadjectives are derived from adjectives with the suffix –tes.
Superlatives ("most") can be formed by placing shú before the adjective; use pe "at, in" for the standard
Man can be placed before adjectives (and other words) to mean "kind of", referring either to degree or indicating that the word doesn't quite apply (nel can also be used in this sense). It can also be used to reverse the comparison for more-comparatives and excessives. (nel TODO)
Súshlites indicates a smaller set of things that it's being compared to. It's roughly equivalent to English comparatives that don't have an explicit standard, or to the word "relatively".
Use láletes (or láleletes) before the adjective for excessives ("too"), and málites for "enough" or "so", and la·le·tes man for "not enough". To specify that something is too/enough/not enough for some particular person or for some particular cause, specify it with the preposition hu if it's a noun, or hi if it's a clause (this clause uses the subjunctive with laletes). Malites can also be used to refer to whatever amount or quality is relevant to the context.
Put ngíntes before the adjective to mean "medium" (TODO)
Ngáltes means "within the expected range", and ngyúntes means "outside the expected range". For instance, a ngaltes tall person might be a basketball player or shorter, whereas a ngyuntes tall person would be a giant.
Tas focuses the degree of the adjective. (TODO figure this out in more detail.)
Las and sáptes← mean "no longer". Saptes is used when unfocused or when focusing on the fact that the adjective did, at one point, apply; las is used when focusing on the fact that the adjective doesn't currently apply.
Ípwetes→ and mimúntes refer to things that do not apply at the time being talked about, but will apply at some future time. Í·pwe·tes is non-focused; mi·mún·tes focuses more on the fact that the adjective does not yet apply, and has less implication that it will at some point.
Múngi refers to something that isn't necessarily going on at the time being talked about, but tends to happen sometimes.
Lil indicates that an adjective applies to the type of the thing instead of the thing itself. It's most often used with an indicator of quantity: Lil hí means "one type", Lil íhe means "many types".
Petútes (vertically), náttes (left-and-right), and lákutes (front-and-back), málnites (horizontally in general) are used with adjectives (including numbers) that describe size, indicating which dimension the word is describing. E.g., mungites wa means "short" (though one could also just say ngi).
Adjectives can be doubled to intensify them. For instance, híleng = purple, híleng híleng = very purple. Less commonly, the second word in a phrasal verb can be doubled (e.g., lú niuspe niuspe = "I am very happy"). Adjectives can also be tripled, quadrupled, etc., for greater intensity, though this is less formal.
Using two opposite adjectives means something in between. In some cases, there are more specific words usually used instead: lat = medium-sized (= húli wa), taustu = warm (= nalken nump)
Adjectives can be modified with a prepositional phrase to indicate a comparison. This is generally used after swa or in a relative clause. Kel "from" is used for greater-than ("more") comparisons, and nel "like" for equality ("as") comparisons.