Merlin Consonants (μ, ρ, λ, ν)
Merlin is shorthand that refers to the nasal consonants μ and ν and the liquid consonants ρ and λ. These consonants behave in certain ways when they interact with certain sounds in certain environments.

Merlin and σ in Verb Stems
When forming verb stems, /σ/ drops when it is added to a base ending in a Merlin consonant. When this happens, the previous vowel stretches:
ἐ/γαμ/σ/α > ἔγαμ_α > ἔγημα
L/ἀρ/σ/α > ἦρ_α > ἦρα
L/ἀγγελ/σ/α > ἤγγελ_α > ἤγγειλα
ἐ/μεν/σ/α > ἔμεν_α > ἔμεινα

Merlin and σ in Noun and Adjective Stems
However, when forming noun and adjective stems, the reverse occurs. Namely, –ν/ drops before /ς. As above, the previous vowel stretches:
λέγ/σ/αντ/ς > λέξαντς > λέξανς > λέξας (where α is long)
Complicatedly, when forming a participle like ἀγγέλ/σ/αντ/ς, the aorist marker /σ/ drops, stretching the preceding ε, because ἀγγελ/ is a verb stem. But after τ drops ν also drops before /ς, stretching the preceding α, because –αντ/ς belongs to an adjective stem:
ἀγγέλ/σ/αντ/ς > ἀγγείλ/αντ/ς > ἀγγείλ/αντς > ἀγγείλ/ανς > ἀγγείλας
(where the last α is long)

Merlin Futures
When forming the future, bases ending in a Merlin consonant usually use a /ε/ future time marker rather than /σ/:
ἀγγελ/ε/ω > ἀγγελέω (Attic ἀγγελῶ after contraction)
βαλ/ε/ω > βαλέω (Attic βαλῶ after contraction)
μεν/ε/ω > μενέω (Attic μενῶ after contraction)
τεμ/ε/ω > τεμέω (Attic τεμῶ after contraction)
φθερ/ε/ω > φθερέω (Attic φθερῶ after contraction)
Occasionally but rarely a base will use /σ/ but with η intervening between the base and the future time marker:
ὀφειλ/σ/ω > ὀφειλήσω
χαιρ/σ/ω > χαιρήσω

Merlin Consonant Clusters
For ease of articulation clusters of Merlin consonants may be broken up by inserting δ:
ἄνρ/Ṇ > ἄνρα > ἄνδρα
The following is rare, but if the Merlin consonant that follows δ is a labial, the dental δ assimilates by becoming the labial β:
μλο/σκ/ω > μλώσκω > μδλώσκω > μβλώσκω > βλώσκω
In the case of μβλώσκω, μ- drops because the cluster μβλ- is too difficult to pronounce at the beginning of a word. See also ἀμβροσία, “immortality,” whose root is μρτ/, “death.” The use of alpha privative results in the following syllabification: ἀμ-βρο-σί-α. This makes the cluster μβρ possible to pronounce.

Stop Merlin Bases
Single syllable verb bases that consist of a stop consonant and Merlin consonant will include α. In some environments, that α appears between the consonants. In other environments, it appears after the cluster:
βαλ/ or βλα/
θαν/ or θνα/
ταμ/ or τμα/ (also basic e-grade τεμ/)
The alternate bases βλα/ and τμα/ are used in the perfect aspect and with the passive marker /θη/ (thus, the future passive and the aorist passive). So for instance βαλ/ε/ω > βαλέω but βλα/θησ/ομαι > βληθήσομαι. The alternate base θνα/ is used in the progressive (ἀπο/θνα/ισκ/ω > ἀποθνῄσκω) and perfect (θε/θνα/κ/α > τέθνηκα).
Merlin and Syllabification
In the syllabification of words, a consonant cluster consisting of a stop consonant followed by a Merlin consonant may be considered a single unit or divided. In other words, δάκρυ may be syllabified δάκ-ρυ, where δάκ- is a heavy syllable, or δά-κρυ, where δά is a light syllable. The gives poets some flexibility when composing poetry. Compare the following verses:
| τὸν δ’ ἠμείβετ’ ἔπειτα Θέτις κατὰ δάκρυ χέουσα. |
| And then Thetis responded to him, shedding a tear. |
| τὸ γὰρ φιλῆσαι τὸν θανόντ’ ἄγει δάκρυ. |
| Indeed, loving the man who died brings a tear. |
In the first passage from Homer, δάκρυ is segmented δάκ-ρυ. In the second from Euripides, it is δά-κρυ. Both serve the needs of the meter (dactylic hexameter in the case of Homer, iambic trimeter in the case of Euripides).
Read more on syllabification here.